[techhead]

After some testing on a clean x-cart installation (no mods) I couldn't replicate this issue.

In order to allow users to register via the checkout I had to remove a couple of lines of code in the include/register.php that was asking for the validation of b_lastname and b_firstname... even though they were not being used.

I can only assume that somewhere in my mad tinkering with x-cart's code I've broken something that is effecting the registration of users in the checkout process.

Thanks for the tip about removing the fields from the template! Worked like a charm.