Also forgot to mention that the error always pops up while it's working on Step #3 "Resolve Machines to Scan".
Verify you are running NetChk 7.8 and its patch (http://www.shavlik.com/downloads.aspx)
Please verify the console machine is activated.
Reboot the machine, next, perform the Help -> Refresh Files
Scan the NetChk console machine itself.
What are the results of the new scan?
If you still have issues, set the logging options to ALL, reproduce the issue and email the logs to support.