[AccessD] combo box not displaying data

Access2000/2003, Win XP

I have a combo box with a union query as a row source.  There are two 
criteria based on data from other fields.  The combo box was working great 
as of last night.  This morning, it will not show the data -- it's showing 
no rows.   I've made no changes to the database since the last time I put in 
new data using this combo box.


The union query itself works fine -- I pasted the sql into a new query and 
it shows the correct data.   Each half of the union query works fine.

The combo box works fine with a different backend, but not the one I need to 
use now.

 I did a compact and repair on the "bad" backend -- no change.

I've deleted the links to the tables and relinked the backend -- no change.

I've imported all the tables into a new mdb -- no change.

I've taken the tables from the "working" version that are common to both and 
the specific tables from the "bad" backend and combined them into a new 
mdb -- no change.

I've tried using Access2003 -- no change.

None of the records in the backend looks screwed up.


I'm afraid my only option now is to create a new backend from the version 
that works and re-enter all the data.

Does anyone have any other suggestion?


Thanks
Carolyn Johnson
St Louis, MO