R12 User login Error while assigning Customer to the user - APP-FND-02913

Issue :  You get above pop up once you try to assign CUSTOMER in the user form.

Solution : You can assign the CUSTOMER field as below also from backend, which has resolved the issue, but issue may vary in different environments. This is just for information.

exec fnd_user_pkg.UPDATEUSER(x_user_name=>'USER_NAME',x_owner=>null,X_CUSTOMER_ID=>CUSTOMER_ID_ASINPOPOP);

Can also follow How to End-Date/Delete an Applications User (Doc ID 1064798.1)