Usually when a CGI script will run from the commend line but won't run in a browser, incorrect file or directory permissions is the cause, however...
** No such file or directory: exec of /Library/WebServer/CGI-Executables/calendar.pl failed **
That looks more to me that the files are not in the correct location to be run from the web server. I don't know where you'll have to put them on your server, you'll have to check the server software's documentation.
Dan O.
------------------