When syntax errors show up:

The error message below tells you the program had an error. Sometimes a line number and error message will be given which will help you to further diagnose the problem.

Software error: Execution of ./calendar.cgi aborted due to compilation errors.

Check the end of your server's error log for additional messages or run perl -wc filename from the command line to see what is causing the problem. It's often a missing (or mismatched) quote character or a missing semicolon, but could be an incompatibility caused by an earlier version of Perl.