Is the following problem already known? 1) Create a new C++/CLI project in Visual Studio 2005 (eg. a console application). 2) Include the header <boost/thread/mutex.hpp>. That's all. When you build and run the application you see the following Windows error message: "The application failed to initialize properly (0xc000007b). Click on OK to terminate the application." If you build a .NET DLL and try to use it from another .NET application the error message changes to: "is not a valid Win32 application. (Exception from HRESULT: 0x800700C1)" In both cases Windows refuses to load the file. While you normally don't need Boost.Thread in a .NET application I ran into this problem because we have a thin .NET layer on top of a native C++ code DLL. As the DLL makes heavy use of various Boost libraries the header <boost/thread/mutex.hpp> ends up in the .NET DLL. Does anyone have an idea why including this header is a problem? Boris