We have received reports that Battle v Chess (Check vs Mate) doesn't support later versions of Mac OS X (i.e. newer than Snow Leopard).
The symptom is that the CD-Key is requested each time you start the game and accepted only the first time you enter it.
Unfortunately we understand the developer has not updated the game to support later versions of OS X, though you can use the Windows version on a Mac in a Virtual PC environment (e.g. Parallels) running a copy of Windows.