From Google..........

http://www.microsoft.com/learning/books/troubleshooting/access/default.asp

Queries: Selection Criteria
Quick Fix: After running a query I see the following message, "Type mismatch
in expression"

You try to run the query you just created and you see the message, "Type
mismatch in expression." The problem isn't really in an expression but
rather it is caused by incompatible data types used to relate the tables in
the query design. The mismatch doesn't show up until you run the query and
the fields are actually compared.

To solve this problem, be sure to relate the tables in the Relationship
window before you create the query. Mismatches are caught right away in the
Relationships window rather than when the query is run.

hth
Vaya con Dios,
Chuck, CABGx3