The parameter 'token' cannot be a null or empty string

I have a SharePoint 2013 office 365. I have created a hosted app from Visual Studio 2012. Have installed MS office development tool also. But if I write any Client Object Model code in code behind, I am getting error as, "the parameter 'token' cannot be a null or empty string". I have tried lot and researched in Google. But no solution. But without Client Object model, just with the .aspx design it works well. Only with Client Object Model getting error like this.

If I used View page in browser, it shows  "the parameter 'token' cannot be a null or empty string".

If Deployed, or debug it shows assembly error in web config file.

Any help will be appreciated.