Hi, just from the error message in the log file and without any other details about your environment, it's not easy to tell exactly what the problem might be.
You could try running K2 Service as a console application, use the shortcut in the Start Menu, where there is much more detailed logging, and it might make it more obvious what the problem is.

I also saw your other question about the "Authentication failed because the remote party has closed the transport stream" error. Maybe it's time to open a ticket with Nintex support, they can help you.

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I suggest taking a look at the HostServer logs as it may log another error before the Object Reference error that is the actual cause of the issue. 

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@KimberlyL 

I had a look with Nintex support and I am getting the error below which is the first error before starting the service on console mode.

System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a send. ---> System.IO.IOException: Authentication failed because the remote party has closed the transport stream.

 

 

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opened a ticket but they cannot find the issue, spent hours with them they will sent to Labs.

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Are you able to test SQL connectivity from K2 server using UDL file?

https://www.ibm.com/support/pages/how-perform-udl-test-check-sql-server-connectivity

 

If SQL access from K2 is still fine, it could be something in the HostServer.SecurityLabel table according to the stack trace.

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