It seems like there is a limit to the length of the filename you upload.

For example this_is_a_very_long_file_name_and_parts_of_it_will_get_truncated.xls
will be stored as this_is_a_very_long_file_name_and_parts_of_it0

That example is out of my head so it's not 100% accurate but you should understand the problem.

-phil