The web application you are attempting to access on this web server is currently unavailable

By looking into event viewer i came to know that it was an issue with aspnet account , it was not having read  permissions on global assemble cache.
Issue was Resolved by doing the following things
-Assignging permissions to aspnet account on Frame work and Temp directories in windows
-Assigning permissions to aspnet account on application deployed.
-Reinstalling aspnet user by aspnet_regiis -i for framework 2.0.