serial number problem

Hello guys

I was trying to create a goods receipt from data gathered by a delivery.

But when i tried to add these goods receipt (when one of the items is managed by serial numbers) there was a problem: "'serialnumber' for item 'itemcode' in line 1 already exists(in unique field)" . I tried to add this goods receipt manually and I had the same problem but in that case it was like a warning and i could continue the addition.

Do you have any idea of what can i do (maybe to force the addition, or to give to the user the same warning) ???