OSCommerce checkout_process.php error

My recently installed website is: 1, Throwing an error page when the submit order button is pressed: 500 Internal server 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. 2. Customers receive their order confirmation but none of the emails including the main administrator e-mail is receiving the confirmation of an order placement.