Symptoms

Here is the sample error thrown from ControlUtil command:-
System.Net.Sockets.SocketException (0x80004005): No connection could be made because the target machine actively refused it 127.0.0.1:5555
 

Diagnoses

Turned out that this is a special scenario in 3 tier setup (Web, App, Data). Under 3 tier setup, the control registration has to be done at App Server instead of Web Server.
 

Resolution

Run the controlutil command on K2 Server instead of Smartforms server:-
1) Copy the custom control dll to a folder on the K2 server and associated sourcecode.forms.controls.web.sdk and web.shared dll's to the k2 server's bin folder
2) Run controlutil to execute successfully on the K2 server instead of the smartforms server using the host parameters.

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