The Ajust Cost - Item Entries run into endless loop and the Adjmt. Level field keep increasing. This problem can occurs to Navision 4.0 and 5.0.The easiest thing you can check is to Open your Item Card. Press F5 to open the Item List form. Scroll to the first record to check whether you have an item witn blank No. or not. If you found a record with blank No. field, you can safely delete this record. You cannot create an Item record with blank No. but when you use Dataport to import the item, blank No. field is possible.
If the above information cannot help you, probably you have other more headache problem in your Navision. Below are some useful forum posts that may help you but I have no luck to stop the endless loop after trying the methods suggested:
1) Mibuso - adjust Cost - by Item
2) Mibuso - adj. Cost Item entries is too slow