Specify an action manager definition

What causes this issue?

You have tried to process an action manager definiton without
specifying its key. This is not possible.

System Response

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

How to fix this error?

Specify the key of the action manager definition if you want to process
it.

Error message extract from SAP system. Copyright SAP SE.