Have you ever had this type of error when inserting a part into an ASM? cf. PJ "Adding a part in this assembly will create a conflict of references. Can't add."
I tried to make a copy of the play but nothing helped. A colleague had the same problem and tried everything (copying, renaming, etc.), he had to redo his piece. If you had other solutions...
You have to remove all external references from the part then go to external references options and check "allow multiple contexts for parts when editing... "