The problem you experience does not concern Telerik's controls and you can see this by yourself reviewing the stack trace of the error message. The problem is related to proxy configuration settings. You will receive the same error if you execute the lines from the stack trace outside our controls. I suggest you try to change the proxy configuration settings in order to resolve this problem. You can take a look at this article
which I found searching in the Internet. I hope that it will be helpful.
the Telerik team