I think that you have something else going on here. The BOs work the same in an application as they would in a BO library. So that you can troubleshoot where you are having a problem, create a new SF Application, add a BO, map it and build the project and you will see that it works without issue. You can then start bringing over your BOs one at a time to see what the problem was. It could be that your Windows App was not created as an SF application or you could be missing some references. Regardless, it is always best to store your BOs in a library instead of the App assembly anyway. Glad you got it going