Thanks for the provided stack trace.
The first thing I noticed is a bit old version you are using. The current one is Version 2014.3.1218.1 so I guess this might be the cause for your issue.
That is why I would ask you to uninstall your AppBuilder from Windows control panel. Then use this link
to download AppBuilder (I suppose you are using Windows client) and install it.
If this does not help please send us the latest log from %localappdata%\Telerik\BlackDragon\Logs folder produced using our latest client version in a private support ticket
I look forward to your reply.