MS Access Overflow Error

MS Access Overflow Error

I am getting an Overflow error in Access when this line runs
intAT = Nz(DLookup("at_ID", "qryAT", "at_sc_ID=" & Me.sc_ID & " AND
at_OT=0"), 0)
If I add Debug.Print Nz(DLookup("at_ID", "qryAT", "at_sc_ID=" & Me.sc_ID &
" AND at_OT=0"), 0) just before that line, it prints the id number just
fine, but still errors during the assignment on the next line.
I can also get it to work by adding a criterion to the query that limits
all the results to those that occur before a certain day and time. It ONLY
works limiting the query to before that particular time, not after an
earlier time. If any of the records after that time are included, it
overflows again. I have looked at the data that was entered after that
time and it all seems fine, but I am not sure what exactly I should be
looking for. The at_ID associated with the first record that causes it to
fail is 32838 if that helps at all.