Correct Inventory GL Posting

I have not been able to find a way to correct inventory item general ledger posting when prior activity leaves a balance in the general ledger inventory account for a particular item. As an example, we have an item with only two open entries, receipts for 4 units at $25.80 each. The general ledger should show $103.20. When we run a report of the item ledger entries for this item, the total posted to the inventory asset account is $ -804.14 (from earlier errors). All other items are closed and cost adjusted where appropriate. Following the documentation, I tried to do the following to fix the GL postings. I made a positive adjustment for one unit and a negative adjustment for one unit. I applied the negative adjustment to the positive adjustment so the items were not left open. I made the positive adjustment of 854.14 + 103.20 and the negative adjustment for 50.00. Prior to running the adjust inventory cost program, the ledger was correct as a result of these adjustments. When I run the program, it changes the adjusted cost on the negative adjustment back to -25.80 and posts the difference to the general ledger leaving me where I started. Is there any way to enter an adjustment in Navision to correct prior inventory posting errors?