When I tried to open an existing solution of mine in Visual Studion 2010, I found this message. 'name of the project.ccproj' cannot be opened as the type 'ccproj' is not supported by this version of visual studio.
I found that after installation of 'Windows Azure tools for Microsoft Visual Studio 2010' it worked fine.
Again, if you are using a different version and opening a project created on a different version please check for the right version.
The one i used was
http://www.microsoft.com/downloads/details.aspx?FamilyID=5664019e-6860-4c33-9843-4eb40b297ab6&displaylang=en