Make sure you have built Coin before building SoWin. You can substitute another Open Inventor implementation for Coin, but expect to need to tweak source code or compile/link settings if doing so. We try to be as compatible as possible, but it can take a long while between every time we test the compatibility. If you built Coin through the Visual Studio project files under build/, then do the same for SoWin. The project files are in the same location under SoWin. If you on the other hand built Coin from the Cygwin shell using the configure + make process, then proceed in the same way for SoWin. You can not use the configure + make process to build SoWin if you did not build Coin the same way. The necessary coin-config script is not set up and installed if you used Visual Studio to build Coin. See Coin/README and Coin/README.WIN32 for more instructions.