Do not use the prefix "User" when creating a userbox in the userspace of User:UBX.
Input box for hosting userboxes in your userspace
editWant to use the "User" prefix? That is not our problem. Go ahead if it is in your userspace!
Input box for hosting userboxes in the Template namespace
editIt is recommended that you use the "User" prefix when creating userboxes in the template namespace.