Hi
As Mukhtar and Ramakrishna rightly said, yo have to calculate WIP again on this order if the order is fully delivered now or you have done TECO for this order.
See, when we do WIP calculation. system calculates WIP to be posted for the order. This calculation may be positive or negative. Means for example if in the month of July (when the order was in PDLV stage), system calculated the amount of WIP to be posted in that month. But in August (next month) when you will do WIP calculation for the same order, system will calculate amount of WIP to be reversed (which was posted in July as WIP) for this order provided the order is in DLV or TECO status. This is how the system is designed.
Now you have to check two points. First that your order is in DLV or TECO stage and second you have done WIP calculation for this order.
Feel free to revert, if you further face any problem in this.
Regards
Rajneesh Saxena