We are currently doing stocktakes in this system for the first time.  We have had a couple of counts error in the Physical Inventory Review screen when trying to Complete PI.  The error we get is ‘Updating Item ##Inventory ID## in warehouse ##warehouse## quantity available will go negative.’ 

As an example the book quantity is 3 and we are trying to post a physical quantity of 0.  We don’t allow items to go into negative however that is across the whole system.  This has happened on about four of five items out of thousands.  

Any ideas on why?  We have checked Inventory summary/allocations etc and nothing has been allocated. It is a rarely used part and has had the initial adjustment in, then a transfer that is pretty much it.