Business Rule BR308
BR308 This is the top-most (#1) Level so its Level Template must have ParentRequired switched OFF
Each Level has a ParentRequired switch to determine whether each Code in the Level should have a Parent code or not.
As it would not make sense for Codes in Level #1 to have Parent Codes the ParentRequired switch must be left OFF. You need to edit your Level 1 to have ParentRequired = OFF