I was changing my Resolution display and I think that I made it too high and now if I try to launch the game it tries to load but then it says (could not load OpenGL subsystem) Can you please tell me what to do I don't know how to fix this
If you know how to use command line, you can run
tremulous.exe +set r_height 400 +set r_width 640
If you don't know what command line is, then you can just delete your autogen.cfg in
%APPDATA%\Tremulous\base
%APPDATA%\Tremulous\gpp if you are running GPP.
If you don't want to lose all the settings stored in those files, you can just edit those files and change the values of r_height and r_width.
If he's getting that error, it's a safe bet that he's not using a client that does r_wdith and r_height.
Go to %APPDATA%\Tremulous\base\autogen.cfg and add the line seta r_mode 6 to the end.