XD 2.1.4 for Steam version 1.2.1.2 of RACE On now has a problem due to a Steam update. The update fixed the Steam overlay but broke the game as follows.

When you Alt-Tab out of RACE On when you have the XD utility installed, you will not be able to bring the game back up. It does not matter from where you do it (ie. menu, cockpit, car setup screen, etc). The game will either crash when you try to bring it back up, or it will come up invisibly. Removing XD from your installation ‘fixes’ this problem. Hopefully a new version will really correct this soon.

Thanks to HumpheryB on our crew, for bringing it to our attention!

Edit: There appears to be another workaround that lets you keep XD. You can disable the Steam Overlay (Shift+Tab) in the Steam Settings. Once you do that you can start the game and tab out as usual.