Error Code : 0x80070021. The requested page cannot be accessed because the related configuration data for the page is invalid

I have tried everything but I am not able to figure out what is the issue that is causing this problem. I am getting Internal Server Error 500. More details of the error is given below:

I have tried everything that were mentioned in this link and also in this link. But none of the solution works.

I am trying to call a webapi method from another webapi using HttpClient. but I dont know what on earth, I am doing wrong.