Scheduler Issues with DNN 7.3.x
Issue Detail
Lot of logs in Event Viewer related with “Scheduler Exception -Sequence contains more than one matching element”. This occurs when there is a duplicate entry in the WebServers table.
Solution
To verify if this is the issue, go to Host > SQL and run the following SQL query:
SELECT ServerName FROM {databaseOwner}[{objectQualifier}WebServers]
If you see the same entry more than once, you need to run the following SQL query:
DELETE FROM {databaseOwner}[{objectQualifier}WebServers]
Once that has been completed, hover over Tools->Recycle Application Domain to make it work with re-indexing.