the only reason you'd get that error is if you have more member fields than listed in ubb_lib_files.cgi.
FTP into your server, go to the members folder, download 00000001.cgi (number doesn't really matter)
Open it in a text editor, and see how many lines there are (should be minimum 40, most likely less than 70)
Take that number, add 3 for safe keeping (cause some fields can overflow to the next line).
If that is less than 62, do this...
# Open ubb_lib_files
# Find 2 times:
my $maxmemfields = 39; #total fields permitted in member file
# Replace with 2 times:
my $maxmemfields = 62; #total fields permitted in member file w/quickreply
If it's more than 62, put that number in place for the 62 in the step I showed you