VuGen hangs with the pop-up error as "Unexpected Error" when an Action is clicked. The below error messages are seen in the pop-up window.
"System.NullReferenceException: Object reference not set to an instance of an object.
at HP.Utt.CodeEditorUtils.BackgroundRenderers.HighlightRenderer.Draw(TextView textView, DrawingContext drawingContext) ........"
This is a known issue with the Load Runner 12.01.
In order to fix this issue, Please apply the hotfix as provided by the HP R&D team.
You can raise a ticket with HP Software Support team for the hotfix. And also for the steps to apply the hotfix suitable to your environment.