The forwarder is having a problem communicating with subscription manager at address https://mycollector.alsheppard.com:5986/wsman/SubscriptionManager/WEC. Error code is 2150858882 and Error Message is .That's it, no error message. Frustrating. However, removing the IssuerCA, leaving the server and refresh values from the GPO's SubscriptionManager line seems to have resulted in a happy event forwarding service.
I would also check Kerberos is set up on the listening server, or at least the SPN exists.