Did anything get altered with respect to Trusted Locations because of the upgrade? If not, why not just re-create the task under the new server and see if that fixes it? It may be that a file or token needed to authenticate the user is no longer present. IIRC, that would not be the case when you open the db with your OS credentials as the logged on system user credentials are passed from one app to another. Could be a different issue when TS is used to open the db, especially if you're not logged on.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.