When you use the Add Affiliations from Exported File routine, the data file must be in a .txt format. Also, the first value/word in the file must be Idcode.
A common use of the utility would be to use any export routine in FIMS to export Profile data (you must include the Idcode), open the data in Excel and remove or add Profiles from the list. Then use the utility to add an Affiliation code back into FIMS for the Profiles in the list. If you are going to use this list as the basis for import, you must save the file as a tab-delimited .txt file NOT a .csv file.
In some exports the Idcode is the first column value, but the label is not just "Idcode" (e.g. it might say DonorId or GranteeId). You must open this exported file in another application (e.g. Excel or Notepad) to modify the column label to say Idcode . Remember to save it again as a .txt file before running the Add Affiliations from Exported File routine.