* .sln will be built in Xamarin Studio, but not in xbuild

Question

I have a Visual Studio solution containing 16 projects in C #. I also have a separate build.proj file that contains three <Target> s:

• Build that contains the <MSBuild> link to * .sln
• Package that contains <MakeDir> and <CopyCommands> for copying embedded DLL / EXE files along with various data files to the $(StagePath) .
• Deploy , which copies files from the scene path to the deployment path.

I managed to run the xbuild /t:Deploy build.proj to create the * .sln file and copy its files to the appropriate location, until recently, when IT decided to move the My Documents folder to a network drive.

Now, when I try to run this xbuild command, I get a few errors like the one below. (Link to one of the dependencies within the same solution.)

 error CS0234: The type or namespace name `Util' does not exist in the namespace `Contoso'. Are you missing an assembly reference? 

But whenever I do "Build All" on the same * .sln from Xamarin Studio, I get a successful build with 0 errors and 0 warnings. So why can't xbuild find these build links if Xamarin Studio can?