Problem using Managed C++ (.Net 2.0) in .Net 2.0 project in VS2010

I have two projects:

1) a project written in Visual C++ 2005 which targets the .net Framework 2.0.

2) a project in Visual C# 2010 that targets .net framework 2.0 and includes the C++ DLL.

When I build the C# project referencing the C++ assemb开发者_开发知识库ly, I get errors like:

C:\Windows\Microsoft.NET\Framework\v4.0.30319\Microsoft.Common.targets(1360,9): warning MSB3258: The primary reference "ScannerWizard" could not be resolved because it has an indirect dependency on the .NET Framework assembly "mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" which has a higher version "4.0.0.0" than the version "2.0.0.0" in the current target framework.
C:\Windows\Microsoft.NET\Framework\v4.0.30319\Microsoft.Common.targets(1360,9): warning MSB3258: The primary reference "ScannerWizard" could not be resolved because it has an indirect dependency on the .NET Framework assembly "System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" which has a higher version "4.0.0.0" than the version "2.0.0.0" in the current target framework.
C:\Windows\Microsoft.NET\Framework\v4.0.30319\Microsoft.Common.targets(1360,9): warning MSB3258: The primary reference "ScannerWizard" could not be resolved because it has an indirect dependency on the .NET Framework assembly "System.Configuration, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which has a higher version "4.0.0.0" than the version "2.0.0.0" in the current target framework.
C:\Windows\Microsoft.NET\Framework\v4.0.30319\Microsoft.Common.targets(1360,9): warning MSB3258: The primary reference "ScannerWizard" could not be resolved because it has an indirect dependency on the .NET Framework assembly "System.Xml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" which has a higher version "4.0.0.0" than the version "2.0.0.0" in the current target framework.
C:\Windows\Microsoft.NET\Framework\v4.0.30319\Microsoft.Common.targets(1360,9): warning MSB3258: The primary reference "ScannerWizard" could not be resolved because it has an indirect dependency on the .NET Framework assembly "System.Security, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which has a higher version "4.0.0.0" than the version "2.0.0.0" in the current target framework.
C:\Windows\Microsoft.NET\Framework\v4.0.30319\Microsoft.Common.targets(1360,9): warning MSB3258: The primary reference "ScannerWizard" could not be resolved because it has an indirect dependency on the .NET Framework assembly "System.Data.SqlXml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" which has a higher version "4.0.0.0" than the version "2.0.0.0" in the current target framework.

If I make the project 4.0, it doesn't give those errors. Obviously, I shouldn't have to make it target 4.0 to use a 2.0 assembly.

Any idea on how I can fix this?

The C++ project was using the v100 Platform toolset. This makes it depend on 4.0 .NET versions of some libraries. Changing the toolset to v90 solves the problem. You may need to install the v90 toolset if you don't have them...