CubeCart admin problem

[riftlake]

I have installed cubecart on one of mysql databases. the store home page loads up fine but when i go to login to the admin area I get the following page

Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request. Please contact the server administrator, webmaster@riftlakeaquarium.x10hosting.com 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.
Apache/1.3.39 Server at riftlakeaquarium.x10hosting.com Port80



Can someone tell me what has gone wrong

Thanks
Edit:
Someone please help!!! I can access the login page for admin and I can go to the store page within my site. I just get the above error everytime I try to log in to the admin side of things which sort of makes the whole thing useless.

[Slothie]

Check the error log in cpanel.

[riftlake]

This is what the error log has to say:

[Sun Nov 11 00:48:25 2007] [error] File does not exist: /home/riftlake/public_html/500.shtml
[Sun Nov 11 00:48:25 2007] [error] Premature end of script headers: /home/riftlake/public_html/store/admin/login.php