While not certain, I suspect the server may have an older version of CGI.pm installed. Perhaps a fellow monk knows when Vars was added to CGI.pm. If you can get a look at the CGI.pm source on your server, search for the Vars subroutine. You should be able to determine the version of CGI by printing $CGI::VERSION. Install the newest version from CPAN if you can. Try a Super Search on Vars
If all else fails you could bother the author, but wait a few days for a reply here first.
Charles K. Clarkson