It seems that the license of the JustMock Trial, that you have downloaded on 16th of December 2012 is now expired. In order to remove the popping up dialog box, you would need to either buy JustMock Commercial license or uninstall the version you are currently using and replace it with a JustMock Lite(which is free but not supporting elevated testing). You could read more about it here
I hope this helps.
All the best,
the Telerik team
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