You can solve this error by remove the file /ContactForm/MessageList.aspx
The file was included by accident. Note however that you are using the pre-compiled deployment files, they are meant for production deployment rather than working in Visual Studio, and the presence of this file causes no error on production environments, it only causes an error because Visual Studio tries to compile it, but nothing needs to be compiled because the deployment files are already compiled, there is no C# source code included.
If you want to work in VS I recommend use the source code package and then learn to produce your own build for deployment.
Hope it helps,
Joe