Field Validation Error Message not correct - User Object

Hi -

I have put a field validation rule on out of the box field of Business Unit on the User Object.

Default Value = 'FS-US'

Field Validation: [<BusinessUnit>]= 'FS-US' OR 'OCS-US'

Field Validation Error Message: Business Unit - Valid values are either 'FS-US' OR 'OCS-US'

When we test the action out when creating a new user and enter FS (not a valid value) we get the error message of:  <?> SBL-DAT56810 NOT our error message.

If I don't make the field required and then save the record and edit the field our message is visable instead of the OOB message.

Any ideas ???