There was a compilation error while loading the UBB.classic libraries and data files:

Can't locate /var/www/cgi-bin/ubb/vars_display.cgi in @INC (@INC contains: ./Modules . /usr/local/lib64/perl5 /usr/local/share/perl5 /usr/lib64/perl5/vendor_perl /usr/share/perl5/vendor_perl /usr/lib64/perl5 /usr/share/perl5) at ultimatebb.cgi line 129.

Please make sure that you uploaded the CGI and Variables files to the proper directory, permissions are set properly on the files, and that paths in the control panel are set correctly.