For DFSORT: "Summary fields must not be control fields. They must not overlap control fields, or each other, and must not overlap the RDW."
The simplest thing to do would inrec duplicate the one field into two and sort on one and sum on the other.
You do realize that your input:
and your output would be:
because if the key is different, they won't sum together.
As William pointed out, you can't overlap sort and sum fields, but it usually doesn't make any sense to do that. SUM is used to sum fields with the same key. In your case, you just show two numeric fields with no key, so I suspect what you really want to do is just get an overall total for your numeric fields. You wouldn't do that with SUM. Instead, you'd do it like this: