In transaction KP06, go to Extras -> Excel Planning - > Upload... There is a field on this screen(program KPP_FLEX_UPL) called File Descriptions. The search help for this field shows a list of file descriptions that is used by the program to map excel fields so that the program knows what the excel spreadsheet looks like when uploading.
I could not find where it is that you define the file description for this program, if anybody has worked on a similar thing, let me know.
Regards,
Vijay