Sigh. SUM FIELDS=NONE cannot be used with a COPY operation. It can only be used with a SORT or MERGE operation. That's because SUM FIELDS=NONE eliminates duplicates and we need a key to determine duplicates. COPY does NOT have a key.
If you want to remove duplicates based on the first 24 bytes as the key, replace your SORT FIELDS=COPY statement with:
Alternatively, you could use the SELECT operator of DFSORT's ICETOOL to do the same thing.