>>Are there any memo fields in the column list?
>
>Yes, I just found it as the same time. This is what is causing this. So, if I have to include all the fields in the GROUP BY clause, but can't include memo fields, what should I do?

In general you've to do grouping and get only key fields plus aggreagate columns. After that you join result of that query back to the source table to get the rest of fields.
Sorry, I've to go. Good night.