problems with pay pal

[ilciof]

i set up the pay pal module, but when i tested it by simulating the buying process when clicking on thr link "pay with pay pal" the browser goes to this address:

 

http://www.bestweboffers.it/modules/paypal/express_checkout/submit.php

 

and what i get is:

 

Internal Server Error

 

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator at [email protected] to inform them of the time this error occurred, and the actions you performed just before this error.

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

 

 

thank you for your help