The Username Or Email You Have Chosen Already Exists

When a new customer creates an account and then tries to place an order, they receive the follow notification after entering their Billing address information during checkout:

The username or email you have chosen already exists. Please try another one.

I have tried changing registration requirements, allowing/disallowing anonymous checkout, logging out and in again, acting on behalf of the customer- I can’t get the error to go away.

It looks to me like CS-Cart is considering the user a guest, even though they have created an account and are logged in. So when they checkout and enter their Billing information, CS-Cart tries to create a new account for them, but can’t because their account already exists.

Any ideas?

The site is if you’d like to try it yourself.

Thanks for your help,


I receive complaints from customer about this error now and then, but I can't replicate it by myself. What's the reason of this error?