I'm having trouble tracing the cause of a notification message failure generated by warehouse center. Completion and error Notifications have been sent to my inbox untill yesterday and thereafter every single notification failed. I can't determine what changed on my DB2 server since then.
The message looks like this

QL10007N Message "8480" could not be retrieved. Reason code: "4".
The explination in the DB2 online help is not very helpful!
Any help appreciated