I have an existing TFS project that has a structure similar to this :
I created a solu
Check if you have any project dependencies set up on your solution. Right click on the solution and select Project dependencies.
See: http://social.msdn.microsoft.com/Forums/en-US/msbuild/thread/562ae95f-e042-45c2-9821-62cac49d0152
If these errors are when you're building using Team Build, check your build definition and make sure that the "framework" folder is included in the buidl workspace. You should also make sure that the relative paths in the build workspace are the same as your local machine.
To chech the build definition workspace right click on the build definition in team explorer and select "Edit build definition" then select the workspace tab. This will show the mappings between the folders in TFS and what the build pulls down to the build server
Go to Solution Explorer. Find your project, right click and select Add Items to Folder. Select your missing Project to add it to the sln.