Upgraded to Visual Studio 2013, and now your Sitecore project can no longer find namespaces?

It seems like Visual Studio 2013 does things a bit differently.

This is not directly related to Sitecore - but it is related to having a web.config inside your project folder.

The problem seems to be, that Visual Studio 2013 starts to parse web.config, and if it finds any errors, or any mismatches (like a web.config that does not match the version of Sitecore, or some ASP.NET references doesn't match) - Visual Studio will start marking every namespace as invalid, even though intellisense works fine.

If this happens to you - try and renaming web.config to confirm that this is what is causing the problem for you.

If it is, try and use a clean web.config from the version of Sitecore you are using, to see if that works.

If it works - compare the two versions of web.config and see what is different, and work your way from here, untill you find what is causing this.

A hint might be to look at assemblybindings ;-)