Need Guestbook 1.5 HELP!

HI everyone, I am having a problem installing guestbook 1.5 and although i browsed these forums i just cant find the answer i need. i installed the program, but when i try a test post or administrator login i get the following message:
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Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.
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now i am not sure what the problem is exactly, but i suspect it is the "guestbook.pl" file, which is in the "cgi-bin" folder where it belongs. however the guestbook is still not functioning properly. i just dont know what to do at this point but tinker with the "guestbook.pl' file as much as i can without screwing things up too bad. can anyone help or has anyone gone through this before? let me know what i am doing wrong. thanks in advance.............

have you changed the file attribut to 755 for execution?