Seeing the following error in the Notification Server logs:
Process: AtrsHost.exe (9128)
Thread ID: 8912
Description: Unable to processing incoming tickle connection: System.Exception: Unable to read client xml "<clientRequest resourceGuid="WL-HDY4771" />
In another incident the server being used as a task server was not listed in the task server collection or the approved task server collection.
Check the to make sure that the server acting as the task server is listed in the task server collection and the approved task server collection.
Notification Server 6.0.6074
Task Server 6.0.1356