[AccessD] Criteria Question

Within my table I have a field that is set to Yes/No format.  I am
attempting to create a query that prompts the user to enter Yes or No as
a criteria for this field.  Everytime I prompt the user and they enter
Yes or No in the prompt box, they get an error of

"This expression is typed incorrectly, or is to complex to be
evaluated."

But yet if I type in Yes or No in the actual query criteria it works
just fine.  I just get this error when I prompt the user to enter the
criteria.

Anybody have any ideas?

TIA,

Mike