Generally when you sum and group by, you must include only the columns in the select that are grouped by.
For example,
select f1, f2, f3, sum(f4) group by f1
will fail because f2 and f3 aren't in the group by clause.
Send me what you are trying to do and I will take a look, however, I wouldn't call myself an access expert at all....
send it to kpierce@drummondco.com and i will take a look at it some time at work tomorrow.
Kirk