diff --git a/src/qqq/components/processes/BulkLoadFileMappingField.tsx b/src/qqq/components/processes/BulkLoadFileMappingField.tsx
index 1e6d82b..b5457b3 100644
--- a/src/qqq/components/processes/BulkLoadFileMappingField.tsx
+++ b/src/qqq/components/processes/BulkLoadFileMappingField.tsx
@@ -131,11 +131,18 @@ export default function BulkLoadFileMappingField({bulkLoadField, isRequired, rem
 
    //////////////////////////////////////////////////////
    // build array of options for the columns drop down //
+   // don't allow duplicates                           //
    //////////////////////////////////////////////////////
    const columnOptions: { value: number, label: string }[] = [];
+   const usedLabels: {[label: string]: boolean} = {};
    for (let i = 0; i < columnNames.length; i++)
    {
-      columnOptions.push({label: columnNames[i], value: i});
+      const label = columnNames[i];
+      if(!usedLabels[label])
+      {
+         columnOptions.push({label: label, value: i});
+         usedLabels[label] = true;
+      }
    }
 
    //////////////////////////////////////////////////////////////////////
@@ -180,6 +187,7 @@ export default function BulkLoadFileMappingField({bulkLoadField, isRequired, rem
       }
 
       bulkLoadField.error = null;
+      bulkLoadField.warning = null;
       forceParentUpdate && forceParentUpdate();
    }
 
@@ -192,6 +200,7 @@ export default function BulkLoadFileMappingField({bulkLoadField, isRequired, rem
       setFieldValue(`${bulkLoadField.field.name}.defaultValue`, newValue);
       bulkLoadField.defaultValue = newValue;
       bulkLoadField.error = null;
+      bulkLoadField.warning = null;
       forceParentUpdate && forceParentUpdate();
    }
 
@@ -205,6 +214,7 @@ export default function BulkLoadFileMappingField({bulkLoadField, isRequired, rem
       bulkLoadField.valueType = newValueType;
       setValueType(newValueType);
       bulkLoadField.error = null;
+      bulkLoadField.warning = null;
       forceParentUpdate && forceParentUpdate();
    }
 
@@ -287,6 +297,12 @@ export default function BulkLoadFileMappingField({bulkLoadField, isRequired, rem
                   }
                </Box>
             </Box>
+            {
+               bulkLoadField.warning &&
+               <Box fontSize={smallerFontSize} color={colors.warning.main} ml="145px" className="bulkLoadFieldError">
+                  {bulkLoadField.warning}
+               </Box>
+            }
             {
                bulkLoadField.error &&
                <Box fontSize={smallerFontSize} color={colors.error.main} ml="145px" className="bulkLoadFieldError">
diff --git a/src/qqq/components/processes/BulkLoadFileMappingForm.tsx b/src/qqq/components/processes/BulkLoadFileMappingForm.tsx
index bacf001..9ea436e 100644
--- a/src/qqq/components/processes/BulkLoadFileMappingForm.tsx
+++ b/src/qqq/components/processes/BulkLoadFileMappingForm.tsx
@@ -298,6 +298,9 @@ function BulkLoadMappingHeader({fileDescription, fileName, bulkLoadMapping, fiel
    {
       bulkLoadMapping.hasHeaderRow = newValue;
       fileDescription.hasHeaderRow = newValue;
+
+      bulkLoadMapping.handleChangeToHasHeaderRow(newValue, fileDescription);
+
       fieldErrors.hasHeaderRow = null;
       forceParentUpdate();
    }
@@ -470,19 +473,29 @@ function BulkLoadMappingFilePreview({fileDescription, bulkLoadMapping}: BulkLoad
                      {
                         const fields = bulkLoadMapping.getFieldsForColumnIndex(index);
                         const count = fields.length;
+
+                        let dupeWarning = <></>
+                        if(fileDescription.hasHeaderRow && fileDescription.duplicateHeaderIndexes[index])
+                        {
+                           dupeWarning = <Tooltip title="This column header is a duplicate.  Only the first occurrance of it will be used." placement="top" enterDelay={500}>
+                              <Icon color="warning" sx={{p: "0.125rem", mr: "0.25rem"}}>warning</Icon>
+                           </Tooltip>
+                        }
+
                         return (<td key={letter} style={{textAlign: "center", color: getHeaderColor(count), cursor: getCursor(count)}}>
                            <>
                               {
                                  count > 0 &&
                                  <Tooltip title={getColumnTooltip(fields)} placement="top" enterDelay={500}>
                                     <Box>
+                                       {dupeWarning}
                                        {letter}
                                        <Badge badgeContent={count} variant={"standard"} color="secondary" sx={{marginTop: ".75rem"}}><Icon></Icon></Badge>
                                     </Box>
                                  </Tooltip>
                               }
                               {
-                                 count == 0 && <Box>{letter}</Box>
+                                 count == 0 && <Box>{dupeWarning}{letter}</Box>
                               }
                            </>
                         </td>);
diff --git a/src/qqq/models/processes/BulkLoadModels.ts b/src/qqq/models/processes/BulkLoadModels.ts
index 9acbc13..955e355 100644
--- a/src/qqq/models/processes/BulkLoadModels.ts
+++ b/src/qqq/models/processes/BulkLoadModels.ts
@@ -43,6 +43,7 @@ export class BulkLoadField
    wideLayoutIndexPath: number[] = [];
 
    error: string = null;
+   warning: string = null;
 
    key: string;
 
@@ -50,7 +51,7 @@ export class BulkLoadField
    /***************************************************************************
     **
     ***************************************************************************/
-   constructor(field: QFieldMetaData, tableStructure: BulkLoadTableStructure, valueType: ValueType = "column", columnIndex?: number, headerName?: string, defaultValue?: any, doValueMapping?: boolean, wideLayoutIndexPath: number[] = [])
+   constructor(field: QFieldMetaData, tableStructure: BulkLoadTableStructure, valueType: ValueType = "column", columnIndex?: number, headerName?: string, defaultValue?: any, doValueMapping?: boolean, wideLayoutIndexPath: number[] = [], error: string = null, warning: string = null)
    {
       this.field = field;
       this.tableStructure = tableStructure;
@@ -60,6 +61,8 @@ export class BulkLoadField
       this.defaultValue = defaultValue;
       this.doValueMapping = doValueMapping;
       this.wideLayoutIndexPath = wideLayoutIndexPath;
+      this.error = error;
+      this.warning = warning;
       this.key = new Date().getTime().toString();
    }
 
@@ -69,7 +72,7 @@ export class BulkLoadField
     ***************************************************************************/
    public static clone(source: BulkLoadField): BulkLoadField
    {
-      return (new BulkLoadField(source.field, source.tableStructure, source.valueType, source.columnIndex, source.headerName, source.defaultValue, source.doValueMapping, source.wideLayoutIndexPath));
+      return (new BulkLoadField(source.field, source.tableStructure, source.valueType, source.columnIndex, source.headerName, source.defaultValue, source.doValueMapping, source.wideLayoutIndexPath, source.error, source.warning));
    }
 
 
@@ -431,7 +434,7 @@ export class BulkLoadMapping
             {
                if (existingField.getQualifiedName() == bulkLoadField.getQualifiedName())
                {
-                  const thisIndex = existingField.wideLayoutIndexPath[0]
+                  const thisIndex = existingField.wideLayoutIndexPath[0];
                   if (thisIndex != null && thisIndex != undefined && thisIndex > maxIndex)
                   {
                      maxIndex = thisIndex;
@@ -506,7 +509,7 @@ export class BulkLoadMapping
                   namesWhereOneWideLayoutIndexHasBeenFound[name] = true;
                   const newField = BulkLoadField.clone(existingField);
                   newField.wideLayoutIndexPath = [];
-                  newAdditionalFields.push(newField)
+                  newAdditionalFields.push(newField);
                   anyChanges = true;
                }
             }
@@ -515,7 +518,7 @@ export class BulkLoadMapping
                //////////////////////////////////////////////////////
                // else, non-wide-path fields, just get added as-is //
                //////////////////////////////////////////////////////
-               newAdditionalFields.push(existingField)
+               newAdditionalFields.push(existingField);
             }
          }
       }
@@ -531,7 +534,7 @@ export class BulkLoadMapping
                ////////////////////////////////////////////
                // fields from main table come over as-is //
                ////////////////////////////////////////////
-               newAdditionalFields.push(existingField)
+               newAdditionalFields.push(existingField);
             }
             else
             {
@@ -540,7 +543,7 @@ export class BulkLoadMapping
                /////////////////////////////////////////////////////////////////////////////////////////////
                const newField = BulkLoadField.clone(existingField);
                newField.wideLayoutIndexPath = [0];
-               newAdditionalFields.push(newField)
+               newAdditionalFields.push(newField);
                anyChanges = true;
             }
          }
@@ -564,7 +567,7 @@ export class BulkLoadMapping
 
       for (let field of [...this.requiredFields, ...this.additionalFields])
       {
-         if(field.valueType == "column" && field.columnIndex == i)
+         if (field.valueType == "column" && field.columnIndex == i)
          {
             rs.push(field);
          }
@@ -572,6 +575,68 @@ export class BulkLoadMapping
 
       return (rs);
    }
+
+   /***************************************************************************
+    **
+    ***************************************************************************/
+   public handleChangeToHasHeaderRow(newValue: any, fileDescription: FileDescription)
+   {
+      const newRequiredFields: BulkLoadField[] = [];
+      let anyChangesToRequiredFields = false;
+
+      const newAdditionalFields: BulkLoadField[] = [];
+      let anyChangesToAdditionalFields = false;
+
+      ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+      // if we're switching to have header-rows enabled, then make sure that no columns w/ duplicated headers are selected //
+      // strategy to do this:  build new lists of both required & additional fields - and track if we had to change any    //
+      // column indexes (set to null) - add a warning to them, and only replace the arrays if there were changes.          //
+      ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+      if (newValue)
+      {
+         for (let field of this.requiredFields)
+         {
+            if (field.valueType == "column" && fileDescription.duplicateHeaderIndexes[field.columnIndex])
+            {
+               const newField = BulkLoadField.clone(field);
+               newField.columnIndex = null;
+               newField.warning = "This field was assigned to a column with a duplicated header"
+               newRequiredFields.push(newField);
+               anyChangesToRequiredFields = true;
+            }
+            else
+            {
+               newRequiredFields.push(field);
+            }
+         }
+
+         for (let field of this.additionalFields)
+         {
+            if (field.valueType == "column" && fileDescription.duplicateHeaderIndexes[field.columnIndex])
+            {
+               const newField = BulkLoadField.clone(field);
+               newField.columnIndex = null;
+               newField.warning = "This field was assigned to a column with a duplicated header"
+               newAdditionalFields.push(newField);
+               anyChangesToAdditionalFields = true;
+            }
+            else
+            {
+               newAdditionalFields.push(field);
+            }
+         }
+      }
+
+      if (anyChangesToRequiredFields)
+      {
+         this.requiredFields = newRequiredFields;
+      }
+
+      if (anyChangesToAdditionalFields)
+      {
+         this.additionalFields = newAdditionalFields;
+      }
+   }
 }
 
 
@@ -584,6 +649,8 @@ export class FileDescription
    headerLetters: string[];
    bodyValuesPreview: string[][];
 
+   duplicateHeaderIndexes: boolean[];
+
    // todo - just get this from the profile always - it's not part of the file per-se
    hasHeaderRow: boolean = true;
 
@@ -595,6 +662,18 @@ export class FileDescription
       this.headerValues = headerValues;
       this.headerLetters = headerLetters;
       this.bodyValuesPreview = bodyValuesPreview;
+
+      this.duplicateHeaderIndexes = [];
+      const usedLabels: { [label: string]: boolean } = {};
+      for (let i = 0; i < headerValues.length; i++)
+      {
+         const label = headerValues[i];
+         if (usedLabels[label])
+         {
+            this.duplicateHeaderIndexes[i] = true;
+         }
+         usedLabels[label] = true;
+      }
    }
 
 
@@ -635,7 +714,7 @@ export class FileDescription
 
       function getTypedValue(value: any): string
       {
-         if(value == null)
+         if (value == null)
          {
             return "";
          }
@@ -694,13 +773,13 @@ export class FileDescription
 
       if (!this.hasHeaderRow)
       {
-         const typedValue = getTypedValue(this.headerValues[columnIndex])
+         const typedValue = getTypedValue(this.headerValues[columnIndex]);
          valueArray.push(typedValue == null ? "" : `${typedValue}`);
       }
 
       for (let value of this.bodyValuesPreview[columnIndex])
       {
-         const typedValue = getTypedValue(value)
+         const typedValue = getTypedValue(value);
          valueArray.push(typedValue == null ? "" : `${typedValue}`);
       }