Make sure you're not standing inside the bounding box of the mesh, so move a bit backwards first. If that doesn't help - disable 'don't select curves', although I'm not even sure whether than option still exists in MOHRadiant .
This occurs when you clone it and rotate it or accidently move the side the wrong way. It should show up in the game. Go into the game and locate it and remember where it is. Now go back to MOHR and click where you think it is. You should get it.
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