This is a particular DNN issue and is generally caused by missing component in the ..\Portals\_default\EventQueue\EventQueue.config file. To fix the issue simply copy the content between the --- lines to your EventQueue.config. Make sure to replace the following value to from the value of your original EventQueue.config file
efbcd110-e941-410a-96f9-96c74b794ec9
In addition you will also need to change the PrivateKey (D9E266EF75204BD7A867C6091FF7587D) to your own custom value.
---------------------------COPY HERE-------------------------------------
<?xml version="1.0" encoding="utf-16"?>
<EventQueueConfig>
<PublishedEvents>
<Event>
<EventName>Application_Start</EventName>
<Subscribers>efbcd110-e941-410a-96f9-96c74b794ec9</Subscribers>
</Event>
<Event>
<EventName>Application_Start_FirstRequest</EventName>
<Subscribers>efbcd110-e941-410a-96f9-96c74b794ec9</Subscribers>
</Event>
</PublishedEvents>
<EventQueueSubscribers>
<Subscriber>
<ID>efbcd110-e941-410a-96f9-96c74b794ec9</ID>
<Name>DNN Core</Name>
<Address />
<Description />
<PrivateKey>D9E266EF75204BD7A867C6091FF7587D</PrivateKey>
</Subscriber>
</EventQueueSubscribers>
</EventQueueConfig>
----------------------------COPY END--------------------------------------