Error while determining condition table key from document number

What causes this issue?

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

System Response

To retrieve condition or formula data, the system translates the entered
combination of document category and document number into a key value
(KNUMV) for the corresponding table of the conditions (PRCD_ELEMENTS).
For the entered combination, the system cannot find such a key value:
Document category: &V1&
Document number: &V2&

How to fix this error?

Check if the entered combination of document category and document
number is correct.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.