EAS 11.1.2.3.500+ unable to connect to older Essbase servers

I hit the same problem as discussed on the OTN thread 3576783 after apply EPM Patch 500, followed by the Essbase 501 PSUs.

Basically any attempt to connect to an old (in my case 11.1.1.3 Essbase server) results in "Error 0. Your session is not connected to the Essbase agent/server."

I tried removing the server, and re-adding it (which was allowed - so at some basic level it is seeing it) using non-SSO, but still no joy.

I tried fully qualifying the server name, and adding the port, all produced same result.

Appears from the OTN thread that this has been an issue since .500 and suggestion seems to be to roll back the EAS to the .0 release level.