ASP.Net AJAXFileUpload: Cannot deserialize. The data does not correspond to valid JSON

I have followed the article from A to Z. I have changed nothing except the destination path. While clicking upload i am getting these errors.

 Note :

My ajaxfileupload control panel is inside an update panel

Uncaught Sys.ArgumentException: Sys.ArgumentException: Cannot deserialize. The data does not correspond to valid JSON. Parameter name: data