I've seen similar threads with this error but not getting solution of my problem.
In my case, the SMP 3.0 crashed for some unknown reason, after that I restarted the service and even the SMP cockpit was showing 0 users connected, when trying to connect with the Agentry client it says "Already logged in Elsewhere". After that I tried to restart the full Windows server but I'm still getting this error.
I am using SMP SP Level : 03 and WPF 220.127.116.11 Client , i reset client also but still getting same error.
Can you help me please?