eDocument is blocked; Action cannot be executed

What causes this issue?

You want to execute an action on an eDocument, but the system does not
permit it. This happens because:
At least one of the business partners is blocked, or
The eDocument has no business partner in this system and the eDocument
has been completed and has not been changed for at least 100 days.

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?

To be able to execute any action on this eDocument, you need to be
assigned to the required authorization group.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.