Group & already contains function module &

What causes this issue?

This function group is to be used for a change document object, however
it already exists and contains one or more other function modules.
Only the function module <(><<)>OBJECT>_WRITE _DOCUMENT, generated for
the change document object, can be in the generated function group.
The function group of a change document object is deleted and created
again each time the object is generated. Any other function modules
already in the group are deleted.

System Response

The change document object cannot be generated and the import of the
object is canceled.

How to fix this error?

Use a different function group, which does not contain any other
function modules, for the generation.
This is possible only in dialog generations in transaction SCDO.
Remove the other function modules from the function group and repeat the
generation and the import.

Error message extract from SAP system. Copyright SAP SE.