K2 – no task notifications processing due to “Unable to load EventBus Server” error

K2 versions older than Five rely on MSMQ for task notification emails queuing and processing. Sometimes you may see the following scenario:

You start process which supposed to send task notification. Notification not delivered and there is no error messages logged nor in K2 host server log, MSMQ diagnostic log nor in Eventbus.ClientRecorderError table logged at the time of task assignment. Obviously process does not go into error state as notification delivery performed on “best possible effort” principle and not preventing user from completing assigned task using his worklist which can be exposed through different UIs.
At the same time it is possible to see that queue exist and messages gets queued into it (Computer Management snap-in > Services and Applications > Message Queuing > Eventbus > Queue Messages:

If it is not highly loaded production environment you will be able to see that message gets queued per each client event, and you can also see that Message ID gets assigned with increment of 2, with new messages being added to the end of the queue. At this stage you may think that Message Queuing may not run – but this is unlikely as when this service stopped message cannot be placed into queue (that definitely will be logged on K2 side) and you unable to view Queue contents in computer management with the following error:

Other possibility is somehow malformed error message and some glitch in MSMQ service itself – again a bit unlikely as new messages gets queued just fine, but you can try Message Service restart along with removing topmost message from the queue. If that does not help (which most likely will be the case), check the very beginning of your latest K2 host server log (defalut location – “C:\Program Files (x86)\K2 blackpearl\Host Server\Bin”), to verify if it contains the following errors:

In case very beginning of your log contains these error messages:

  • “7030 Unable to create ‘dlx\EventBus’ queue : ‘Message Queue service is not available.'”
  • “7030 Unable to create ‘dlx\EventBus Error’ queue : ‘Message Queue service is not available.'”
  • “EventQueueProcessing.Main”,”7026 Unable to load EventBus Server”

This means that Message Queuing service on K2 server was not running at the time of K2 server start.

To resolve this make sure that Message Queuing service is up and running and restart K2 service – unfortunately there is no other way to reinitialize MSMQ processing thread which gets initialized on K2 service startup.

You may run into this situation after server reboot if K2 service started before Message Queuing service. To prevent this situation from happening you may want to configure K2 service startup to Automatic (Delayed Start) while keeping Message Queuing configured for Automatic start – that will add some delay to K2 service startup as it only will be attempted after all other services configured for Automatic startup will be started, but honestly I don’t see any problem with that – server reboot translates into downtime in any case and slight delay does not make any big difference here. Another, and possible more “fine grained” option to address this is to configure dependency on MSMQ service for K2. To do that run CMD windows in elevated mode and execute the following command:

sc config “K2 blackpearl Server” depend= MSMQ

After successful execution of this command the following dependency for K2 service gets created:

As per MSFT documentation this setting ensures than on machine startup services listed as dependencies are started before attempting to start service which depends on them.

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