You can't include both winsock.h and winsock2.h in the same file. You are probably accidentally including winsock.h via windows.h (winsock2.h is required by enet). If you #define WIN32_LEAN_AND_MEAN before you include windows.h, that should probably fix your problem, or you can set _WIN32_WINNT >= 0x0400. -Kevin Wasserman