please check these link1 and link2
Edit:
I got this fix from.. Hanselman
Browser Definition files shipped with .Net 2.0 and .Net 4.0 contains defintions for certain range of browser versions. By default, ASP.NET uses sniffing technology for the user agent string to detect browsers. The browser definition files cover a certain range of browser versions.As the version numbers increase, ASP.NET might not recognize new versions of a browser by using the user agent string. In this case, ASP.NET might handle these versions as an unknown browser and causes inconvenience.
FIX
The fix is to get updated browser-definition files. You can install a machine-wide fix or just fix individual projects. Hotfixes are availble with download links. - .Net 4 - .Net 2.0