First off, we do not warrant that CO2 will run under Win 10. It should but as we have not yet gone to Win 10 ourselves we cannot test it. We won't be going to Win 10 until we have finished converting our development environment and that may be some time off yet. But the good news is that you should be able to address the error your getting. The mfc100.dll is a code library from Microsoft. It manages their Microsoft Foundation Classes that we use in our game. Please check your CO2 game directory and locate the VS 2010 vcredist_86.exe if you have a 32 bit OS or the VS 2010 vcredist_64.exe if you have a 64 bit OS. (I'm not sure whether Win10 has a 32 bit version but you will need to check that yourself as I don't have a Win10 machine. Then all you need do is double click that exe file and it will install the required dlls. Then run CO2. Please get back to me and let me know how you got on.