Diagnosis
You want to delete a location, a handling unit or a stock item. However,this stock item is still being used and cannot be deleted.
A stock item can only be deleted if there is zero stock.
A location and a handling unit can only be deleted if you have nosublocation/subordinate handling unit and no stock quantity.

Procedure
Display the object contents and, if necessary, book out the stock ordelete the sublocations/subordinate HUs.