If the dialog is present, an error occurs. Add an Event Handler to the Check Existence of Window Test Case that clicks e.g. the cancel button in the window and waits for the window to close. The Event Handler should react to a check failed event, and should use retry as the reentry property. Once the window has closed, the failed Test Step (check existence) will be carried out again. This time, the check will succeed, and the test will continue. The Test Step will be marked as successful on retry.