Output &1 of document &2 has been processed in the meantime

What causes this issue?

You attempted to output message <ZH>&V1&</> of document <ZH>&V2&</>,
but this output has been processed by another application in the
meantime.

System Response

If you execute the message output in the foreground, the system cancels
the edit process. If you start the message output in the background,
the edit process of the current output is cancelled, but other, future
outputs are processed normally.

How to fix this error?

Check the processing status of output &V1& in the output data of
document &V2&. Reissue the output if necessary.

Error message extract from SAP system. Copyright SAP SE.