Thank you for sharing the exacts steps you took with the community.
After 1 spending 1 week trying to fix that problem that came up when I deployed an app to azure, the problem solved when i copied System.Web.Extensions.dll from another pc and pasted to mine in the
C:\Windows\Microsoft.NET\assembly\GAC_MSIL\System.Web.Extensions\v4.0_4.0.0.0__31bf3856ad364e35
directory.