The error occurred when upgrading from version 5.3 to 5.4.

(5.3 version 5.0004.1300.0 -  January 2022 Cumulative Update installed)

(5.4 install version - 5.0005.2000.0)

Host server/bin -log

"5613053","2022-09-28 15:24:47","Error","System","2001","ServerStartError","SourceCode.Hosting.Server.Runtime.HostServerEngine.StartHostServer","2001 Error Starting Host Server: System.InvalidOperationException: Sequence contains no elements
at System.Linq.Enumerable.FirstrTSource](IEnumerable`1 source)
at SourceCode.Hosting.Server.Runtime.HostConfigurationManager.GetClient(IFramework framework)
at SourceCode.Hosting.Server.Runtime.HostServerEngine.StartHostServer()","system","::1","servername:C:Program FilesK2Host ServerBin","5613053","e2bd2baca70142399d64a6391321400b",""

Setup log -

AuthorizationBase.Execute: Logged Error: Failed: System.Net.Sockets.SocketException (0x80004005): No connection could be made because the target machine actively refused it IP:5555

How to fix this?

I try used that method and the error message doesn't change. @Roche 

https://community.nintex.com/t5/K2-Five-Cumulative-Updates-and/An-error-occurs-upgrading-from-K2-blackpearl-4-7-and-K2-Five-5-3/ta-p/215920