OK, I can create the customer/Seller (without filling in the seller info in the Back-Office) and it works. Then I could fill in the seller info. (from front office or ...) Nevertheless, the error (mentioned in previous post) should not happen...
I am not sure what you mean - at back office, when you create a customer account, you are not able to enter seller info, you can only choose "create seller" or not.
The seller info must be entered after the account is created. I am not sure how you can enter seller info when you create customer account, unless you have done customization.