The type 'System.Windows.Input.ICommand' exists in both 'PresentationCore.dll' and 'System.dll'

Question

I\'ve got this error that I just can\'t figure out.

I\'m using VS 2012 (VS11) on Windows 8 with .net4.5 and I get this error when compiling a project that worked wit

Answer 1

Take a look at this similar post, How can I resolve this? The unit type exists in two dll files, it suggests that you are referencing two assemblies with the same type, so you would need to give the type you want to use the fully quantified name.

Answer 2

We had the same problem with our libraries after moving to a new build server.

The solution was to specify the path of the .net framework to build against:

/p:FrameworkPathOverride="C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.0"

If the .net 4.0 framework (Multi-Targeting Pack) is not installed on the build server (as it was with us), you can just copy the "v4.0" folder with all its assemblies to the build server ;)

Answer 3

c:\Windows\Microsoft.NET\Framework\v4.0.30319\System.dll

The message is accurate, ICommand indeed exists in both assemblies for .NET 4.5. The problem is your reference to System.dll, your project is using the wrong one. The assemblies in the Microsoft.NET directory are no longer suitable to act as reference assemblies, like they were in versions of .NET prior to .NET 4.0. They should no longer be there but unfortunately are required to get C++/CLI projects built.

Your reference to PresentationCore.dll is correct, it uses the c:\program files\reference assembly subdirectory. The proper home for reference assemblies in .NET 4.0 and up. These assemblies are special, they contain only metadata and are not a copy of the runtime assemblies.

You'll need to fix your project. System.dll is probably not the only assembly that has this problem. Open the References node of your project and verify them one by one. Remove bad ones that point to Microsoft.NET and replace them with good ones by using Project + Add Reference. Best to just replace them all to be sure.

Answer 4

I had a similar problem with fxcopcmd V12. I was able to solve it by explicitly adding

/reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.0\WindowsBase.dll"

See: FxCop engine exception on WPF assembly