Select query not working

I have a Select Query, the SQL looks like this:
SELECT DISTINCT tblPayments.Yatah! Yatha!, tblCourseSelect. Yatah! Yatha!
FROM tblPayments LEFT JOIN tblCourseSelect ON tblPayments.CourseNumPaidFor=
tblCourseSelect.SelectedCourseNum.
WHERE (((tblPayments.PaymentDate)#6/30/2006#));
This query has worked for over a year on a frontend backend setup, the only
changes have been in the Where statement. Then not on all the computers, but
some are getting 24084 records and the computers that are working as designed
have 1245 records (which is correct). What happened? If I set the quey's
unique values property to "Yes" then the record count goes to 1245 but the
fields in the form that has this query as its source, can not be edited.