Error setting field value, code used to work.

[Monica]

Access 2003 running on XP:

I have a database we've used for two years in our home business. A
few months ago I started getting an error when I clicked a button we
use frequently -- when I ran the mdb on my work computer. Annoying
but not a show stopper.

Today the error started occuring on the home computer - where it is
critical.

The button in question closes the detail form, first refreshing the
main form with the record ID from the subform:

----------------------
' refresh customer lookup list so that we see the new row
[Forms]![KennelCheckIn]![Combo28].RowSource = "sqry_Contacts"

' pass contact id back to checkin form
[Forms]![KennelCheckIn].[ContactID] = Me.ContactID <-- ERROR HERE


' Close contacts form
DoCmd.Close
-----------------------

The error states:

Run-time error '-2147417848 (80010108)':
Method 'Value' of object '_AccessField' failed

Why would this begin failing, and why on one machine months before the
other? When it fails, it crashes Access entirely. No code changes
have been made to our 'production' copy running at home.