Filter by form

I have a form that was created using Access 2000. The filter by form
function would allow the user to enter just a few characters in the field and
then it would display in the drop-down box any records that started with
those characters. We have upgraded to Access 2003 and have lost the ability
to enter just a few characters. When a filter by form is completed and the
form is closed, an error box appears stating that "Microsoft Office Access
has encountered a problem and needs to close", asks if an error report should
be sent to Microsoft and creates a back-up of the form. What is happening?