I get the following error:
Error: Framework \'.NETFramework 4.0 Client Profile\' not installed.
When I try to build my project.
How do
MSBuild projects can reference arbitrary framework profiles (subsets), which will only work if the profile is installed in the runtime's frameworks definitions. Mono doesn't have all of the framework profiles that .NET has, e.g. the .NET 4.0 Client Profile.
To work around this, change the project to use the full 4.0 framework.
In MonoDevelop, here's how you change the setting: