When using SftTree/NET with Visual Studio and you want to use the .NET Framework 4, make sure to not to select the "Client Profile" as it does not offer the necessary support required by our controls. Select any framework version (2.0, 3.0, 3.5, 4.0) as long as it's not the limited Client Profile runtime.
If a "Client Profile" framework is selected (which happens to be the default for VS 2010), the error "Code generation failed for property 'Collection' failed. ..."
In the project settings, select the "Application" tab and select the framework version ("Target Framework"):
In the project settings, select the "Compile" tab and click on the "Advanced Compile Options".
Then select the framework version ("Target framework"):