Hrm... OK, I'm not sure then what the problem is. I suspect it's still somewhere in the event handlers for the form. I think, at this point, I'd contact SmartBear support directly and see if they can give you some insight.
I get the same error... not immediately on TC start up, but when I try to open a keyword test. So, defintiely something in the extension itself.
Did you find the cause of the error in the extension?
Is there any update on this issue you can share?
You are missing an icon for your script extension. Add an icon file and then reference it in your description.xml file. Once you do that you will no longer get the error that crashes TestComplete.
Currently your description file has
<KDTOperation Name = "HNB Property Checkpoint" Category = "Checkpoints" Icon = "">
Once I added an icon file Test Complete no longer crashed. You still have errors in your script extension but at least you will be able to see those and will be able to start working through them.
Hope that helps.