Query linking two fields on form doesn't work

[Carrie]

Hello, I have a front end and a back end for this database. The Enforcement
Subtype is directly related to the Enforcement Type (ie. Enf. Type A can only
have Subtypes 1,2,3 Enf. Type B can only have subtypes 3,4,5....) I built
this query:

SELECT Enforcement_Subtypes.Enf_Subtype_ID,
Enforcement_Subtypes.Enf_Type_ID, Enforcement_Subtypes.Enforcement_SubType
FROM Enforcement_Subtypes
WHERE
(((Enforcement_Subtypes.Enf_Type_ID)=[Forms]![Compl_MAIN_Form]![Enforcement
Type]));

This is the Row Source for the Enforcement Subtype field on the data entry
form. This has been working for almost a year and has suddenly stopped
working. Previously the user would select the Enforcement Type using a
dropdown and then would tab to the Enforcement Subtype field where a drop
down list would only show the appropriate subtypes for this type. It still
is showing the correct subtypes and you can select one; however, it is not
saving them along with the record. When you go back into this record later,
the enforcement type is there but the subtype is missing. (But the really
weird thing is that if you pick the first enforcement type and appropriate
subtype it will save the record)

In checking the backend tables, it seems that the enforcement subtype ID is
being saved for all records - it's just a problem with the form. Any ideas
how to correct this? I thought maybe there was a problem with the
relationships but in opening the relationships window and selecting Show All,
no relationships are appearing (I'm not sure if this is a problem or not
since the rest of the database seems to be working fine).

Really appreciate the help!