Hi,

The situation to end up with a negative cost has always been there when using Weighted Average and performing cancellations or returns.
This is not a unique issue in IFS but the general behavior in the weighted average calculations.
The common issue here is that when using WA and the customer has very different costs for the same part, they can end up with negative inventory value during the process when a part is returned at a higher PO value than the current inventory cost. If the customer has a wide range of costs for a specific part and they know that they will do cancellation of purchase order receipts or returns to supplier, they must be aware of the consequence of having negative inventory value. If they have this situation often and find it not acceptable, then maybe they shall reconsider the use of WA and use another valuation method instead.
It is true that we cannot issue or move a part with a negative cost. This issue exists for almost all issues and deliveries. For example, Normal Issue, customer order delivers and Material Requisition issue.

The only action you can take now is to correct the cost manually for the quantity that is still in inventory. This can be done on the Inventory Part/Cost/Inventory Value subtab through the RMB Modify Level Cost Details.

Hope this helps.