500 Internal Server Error, using e-commerce plugin

I am getting this error when i add products to my shopping cart using wp-ecommerce, its only ever since i had to do a restore from a backup files after losing my sql database. it does make the changes i want but i get this error, any ideas?

Internal Server Error

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

Please contact the server administrator, [email protected] 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 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request.