500 internal server error on magento checkout

Question

Everytime I try to checkout as a user in the magento site I've been working on I keep getting an error. It happens when clicking on the checkout button or by going to /checkout/onepage. Sometimes it will be an internal server error and other times it will show a couple lines of the accordion menu. This only happens when I am logged in as a customer. Checking out as a guest has no issues and registering at the time of checkout also has no issues. You can view the site at wadjetworldwide.com.

Answer 1

I had a similar problem that only showed when i was using a Theme. At the end after testing lots of things the solution was to increase the php memory limit from 32 to 256MB.

=]

Answer 2

Make sure that your php files have the correct permissions. Try 644