Various errors may occur during a script test run: unavailable methods or properties, non-existent windows, and so on. If the Error handling > Show a notification when an unhandled script exception occurs property is enabled in your project, TestComplete will show the Error dialog every time an unhandled exception occurs during the script test run.
In the dialog, click OK to close the dialog and stop the test run. TestComplete will post information on the occurred exception to the test log.