DTS fail when copying a table from one dB to another dB.

The destination table is empty and I copy using DTS the corresponding table from an other dB. (Both databases looks the same . One is a test dB the other production. So the source and destination tabel looks the same
Append rows to destination table is chosen.
Both tables got foreign keys, and Enforce relationship for replication and Enforce relationship for insert and updates are checked. No index or constraints
Atter running it this comes up
"Error at destination for Row number 2359097. Errors encountered so far in this task:1."
This is by the way the last row in the source table.
What can be the problem?