Interesting, that step is part of the 2.0 update, which is re-run to ensure you're properly set to 2.0 first.
It appears that you have a filename with an extension that is longer than expected, i.e., more than 8 characters.
Maybe try to rename it? This sql may help you find the problem filename:
SELECT filename FROM `smf_attachments` WHERE INSTR(REVERSE(filename), '.') > 9 and attachment_type <> 3;