** File does not exist: /home/gwilly/public_html/500.shtml **
That has nothing to do with CalendarScript, check your hosting settings or check with their support.
** Premature end of script headers: /home/gwilly/public_html/cgi-bin/calendar_admin.pl **
That could be caused by just about anything. Check to see if there is a more detailed error message recorded in your error log files or try running the administration script from the command line (telnet, SSH, etc.) to see what errors Perl reports.
Once you have a more detailed error message, post it here is you can't figure out how to correct it.
JMO
Dan O.
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