This is a case where you were not able to change item number of this asset from change item number. This error comes when we use select action "change Item Number" on asset application and assets location is inventory. To resolve this error you need to transfer this item to non inventory location using inventory usage application only. Also you need to select asset number or given full quantity if you want to move all asset attached with same item number and complete this record then asset location will be changed to your mentioned location inventory usage line. Then you will be able to change item no. on asset application.