This dialog is displayed if the Use standalone application from command line by default option has not been selected in the Options dialog, the environment parameter in the command line has not been set and more than one environment has been opened. In this case Code Compare asks you about comparison opening.
This dialog allows you to open your comparison either in the standalone Code Compare or in Visual Studio add-in.
Use standalone application from command line by default
Select this radio button to use the standalone application by default.
Use open environment from the list
Select this radio button to use one of the open environments from the list below.
Select the required environment to open comparison document in.