I've experienced this on many occasions. No amount of editing or re-formatting of columns would fix it.
I had a spreadsheet linked to the Access database that I would use for post-processing (pivot tables, charts, macros, etc). The raw import of new data would go smoothly until I started refreshing the data from the linked spreadsheet. Then, the Subscript out of Range error would start upon the next import of new raw data (during the same session). Only by closing both Access and Excel and re-starting them (not just the files, but the whole program) would the error stop. I think there is a connection between a data-link and the import process such that Access can't update a table if it is actively linked to some other source such as a spreadsheet.