The operation could not be completed.Unspecified error in Visual Studio 2010

Error:

I am unable to open CSS files in Visual Studio 2010 after adding to a project.

It shows the following error:

The operation could not be completed. Unspecified error.

Even if I try to edit embedded CSS in a webpage directly, intelligence doesn't appear.

Solution

I was having the same issue just now 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.

Reference

http://stackoverflow.com/questions/6731470/css-file-not-opening-in-visual-studio-2010-sp1

http://social.msdn.microsoft.com/Forums/en-US/vseditor/thread/25f9016c-c790-4b8a-b333-5cfdafe45e2d