CSS file not opening in Visual Studio 2010 SP1?

I found the solution from here:

I was having the same issue and found that by going to the Tools -> Extension Manager -> Online Gallery and search for/install the "Web Standards Update for Microsoft Visual Studio 2010 sp1" I was able to open CSS files again.

And it worked for me.

Probably it can happen after installing the Visual Studio LightSwitch beta

OR

Windows Azure tools installed

OR

SQL Server 2012 installed

Download this and install it if already installed then repair it and it'll fix the issue:

http://visualstudiogallery.msdn.microsoft.com/a15c3ce9-f58f-42b7-8668-53f6cdc2cd83