More than likely the call off has been allocated to a picklist or a delivery plan in error. You can find this out by doing the following
On the call off in question, click in the Order Quantity field and press F5
Hover your mouse over the 'Quantity Outstanding' field
The tool tip will list a breakdown of the Outstanding items
If it is showing as having items 'Allocated to Picklist', then press F6 to view the picklist or delivery plan number
If this happened in error then follow the steps below to cancel the picklist
Go to Sales
Click on Delivery Menu
Choose Picklist Maintenance
Highlight the picklist found in the instructions above.
Click Cancel Picklist
or these steps if it was allocated to a Delivery Plan
Go to Sales
Click on Delivery Menu
Choose Delivery Plan Maintenance
Highlight the Delivery Plan found in the first instructions
Press F3
A message will show saying 'The Delivery Plan cannot be deleted, as these have call offs allocated to them. Would you like to remove the call off allocations and set the delivery note to cancelled'. Click Yes
