It's going to be a trunk issue. Nothing is COS / COR will have anything to do with it.
You didn't say, but because I've seen this issue on PRI trunks (only) I'll assume you have PRI. Let me know if that isn't correct.
What version of 3300 do you have?
I don't remember the exact fix but the last time I had to deal with this it had to do with a protocol mismatch on the PRI circ.
Perhaps someone else remembers the fix.
Ralph