An option is to delete the allocation records for the sales order. Go to manual sales order allocation, when you have selected the allocation record the system will display DELETE, allowing you to delete the allocation record. This is the easiest option.

If you are talking about a FAS order it sometimes is a bit more complex.

Brad.  There are two ways to remove the zero allocation records so that the zero balance will work.  Firstly as soon as you mark the WO as closed the allocation is no longer required.

The other option is to use menu option 16.13.1 and select the component.  Then look at the detail.  For the record you don't need you need to select it and delete it.

This problem usually occurs when the shop floor pick different materials to the ones suggested (allocated) on th WO.