visual studio 2013 c＃开发的应用程序与Windows 7，vista，Windows 8,8.1不兼容

I have developed a 32 bit Visual C# application in Visual Studio 2013 (using Windows 7 64 bit) that targets the .Net 4 Framework so it runs on Windows XP, Vista, 7, 8, and 8.1. When I deploy the app to my Virtual machines to all those Windows versions, I have to set the compatibility for it to Windows XP Service Pack 2. Why is that? It uses a C++ dll in some of the options if that makes a difference (I compiled the dll with the /MD linking option since it is unmanaged code). Thanks in advance for any replies.I have developed a 32 bit Visual C# application