Server needed a reboot. Lorian just got me on MSN to say "loads of errors from someone called madmclw, looks like they're trying something that isn't working"
(any errors go straight to his email box, so that he can monitor whether the sites he hosts are working, to limit down time)
Anyway, should be ok again now - the operating system had a hissy fit by the look of it!
I think it should be a simple bit of SQL to get the dates sorted out (something along the lines of uploading the old member table to the server then SQL similar to UPDATE new_member_table SET new_member_table.date_joined = old_member_table.date_joined WHERE new_member_table.member_name = old_member_table.member_name for the geeks among you.)