Error when releasing IDoc &1 (return code: &2)

What causes this issue?

An error occurred when unlocking IDoc &v1& (return code: &v2&). It may
be that processing of the IDoc ends with status 30 ("IDoc is ready to
be sent"). In this case the IDoc is not transferred to the port.

System Response

None

How to fix this error?

Contact your system administrator.

Procedure for System Administrators

Contact the SAP Hotline.

Error message extract from SAP system. Copyright SAP SE.