I have webpage which has gridview, one of the columns will have a image. When clicked on image it will open the PDF saved on the web server. It was working fine but I am getting
Your error is specifically to do with 'client impersonation'. I had the same error on one machine but not on another. By comparing settings I worked out the difference.
Start IIS Manager. Select the server in the left pane and double click 'Authentication' under the IIS group in the central pane. Select ASP.NET Impersonation and select 'Disable' at the top of the right pane.