Hi
I got this issue resolved. I had installed asp net Framework 3.5 from Windows Server 2012 > Add Roles and Features Wizard. Then tried to refresh "Server Components" in Plesk, but ASP .NET 2.0 was not detected. Then on further check I found we need to enable ASP .NET 3.5 in "Server Roles > Web Server (IIS) > Web Server > Application Development", after this is done, went to refresh "Server Components" in Plesk, got it enabled in Plesk 11.5 too.
Regards
Anil