[Yagu]

Use /clearrace to exit the buildmode, and then try /joining again.

Also sneaky v0.1a update:
-Prevented passengers from getting /ready
-Prevented using /ready to unready once countdown has started
-Prevented /buildrace when the wannabe builder is participating in a race
-Trying to /ready outside the starting checkpoint now returns the correct error message
-Fixed few situations where race wouldn't start even if everyone was /ready
-Added #defines RACEADMIN and BUILDADMIN which disables some commands from non-admins, uncomment from source to enable
-Players have their builder/racer status removed on disconnect
-Some code cleaning, new functions and such

Check the OP for links.