The :: in ::fieldname indicates that the field is from a different table occurrence than the one specified in Layout setup | Show Records From for this layout. In manage | database | Relationships, you should have a relationship that links the layout's table occurrence to this field's table occurrence. If the relationship is invalid (key field in layout's table is empty) or no related record exists in the related table and "allow creation of records via this relationship" was not selected for this related table in the relationship that links it to the layout's table occurrence, then you will be unable to enter data into this field until this is corrected.
Ugh... Yep.. That makes sense. I see what's its doing. Hmmm... Now how to make it right. Thanks! At least I have a direction ow.