This seems to be a problem with Visual Studio and there has been a lot of people with the same issue on the internet. I have prepared a google search for your convenience. I would suggest to start with this one because it seems that this is the most common solution. I will try and elaborate on it.
Go to \Windows\Microsoft.net\Framework\vXXXX\Config and locate the machine.config file. Go through it and locate the following lines:
Same problem after upgrading to Telerik Data Access Q2 2014. This fixe works.