Message is not the first one in message queue

What causes this issue?

Message is not the first one in message queue. Once all predecessor
messages are successfully finished, it will be processed automatically.

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?

Check status of the first message in this queue by marking the message
entry and click "Related Messages", "Sequence Messages" to see all
messages of a sequence.
Pay attention that when clicking "Sequence Messages" all messages
(including finished messages) of a sequence will be shown. Contrary to
this, when looking at the bgRFC Monitor you only see all incomplete
processing messages.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.