When I tried to build my project in Xamarin Studio (it will build in Visual Studio) that uses several NuGet packages I got following error.
Error: Command 'mono --runtime=v4.0.30319 [Path]/.nuget/NuGet.exe install "" -source "" -RequireConsent -solutionDir "[Path]/"' exited with code: 1. ([Project])
The error occurred because that the path contained one or more spaces. If you download the latest version of NuGet.targets from CodePlex there is a fix for this error. Just replace the code in your NuGet.targets with the code you find here.