SAP Message VF170 - Value of open quantity must not be greater than &

Diagnosis
The open quantity may not exceed the comparison quantity. Thecomparison quantity is figured from the difference of order or deliveryquantity and the previously-billed quantity in order and deliveryreference documents.
In billing reference documents, the comparison quantity is equal to thebilling quantity.
The amount you entered is : &V2&
The comparison quantity is : &V1&

System Response
The system rejects processing of the open quantity you entered.

Procedure
Change the manually-entered open quantity to a positive value that isless than or equal to the comparison quantity.