Unable to delete a PO

SOLVED

Hello everybody, need your help here.

First, I'm using Sage 50 Quantum 2013.

So here's the problem ;

I'm trying to flush 2 PO out of our system but they don't want to go. Here's the error I get :

"Sage 50 can not find the stock part of this transaction. An other user may have erased it. Select an other stock and process the transaction again". (It might not be the exact wording because I translated this from french).

I tried playing around with the stock and nothing works. I even tried to modify the order so it is a totally different stock and still come up with this error.

Anybody has an idea ?