OAuth Error

Hi , Can anyone help me in solving the errror while seeting up OAuth Authentication getting error in redirect Url as 

The server encountered an error processing the request. The exception message is 'Object reference not set to an instance of an object.' 

Here I am attaching the screenshot of configuration of OAuth login Page.

I am getting the exception after allowing permsission and after redirect Url . Should i need to add anything extra in redirect url or how will i get access token based on result of Redirect URL?

Thank You.