All too often, a user get's an error such as
"Fieldx" is defined to require a value....
It isn't clear from which TABLE FieldX is defined. In complex relationships, this costs us time finding the correct field in order to examine it's options. For new users, it can leave them frustrated due to checking the wrong field and not finding the source of the error message.
In any case, it would seem a trivial modification to add just a bit more detail to this error message.