would you happen to have your backup from your previous version? If so, search for $maxmemfields in ubb_lib_files.cgi and write down that number.
Then, open up your 6.7 ubb_lib.cgi
FIND:
$vars_config{'MaxMemFields'} = 43; # maximum profile fields + 1. hard coded. That means it has to be changed here, Allen, not in vars_misc itself. ;)
Change that 43 to the number you wrote down