Supply Subinventory not defaulting in Material Requirements form

Hi Experts,

Supply subinventory is not getting defaulted while changing the material requirements in material requirements form when users are trying to add new component. It is not allowing to delete the initial record also. Displays the error "FRM-40657:Record changed or delete by another user". Subinventory value is populated in WIP parameters. BOM of the WO, Resource and items don't have any supply subinventory value populated. What could be the probable reason for this issue? Pls let us know your inputs on this.

Thanks