This issue is caused by the Column properties in Excel not in the correct (Text) format.
To correct this, save your Excel file as a .CSV file.
Once saved open a New Excel Workbook. In this Workbook click Data > Get External Data > Import Text File.
- Step 1 in the Text Import Wizard - Select Delimited
- Step 2 in the Text Import Wizard - Delimiters need to be set to Tab & Comma
- Step 3 in the Text Import Wizard - Column data format must be set to Text. Be-sure to select each column an set Column data to Text.
Once the Data is imported Save your new Workbook as and .xls
Now re-map your label file to the New Data source file you've created.