Today, while I was riding home, I started to feel a wiggle in my cranks, so I pulled over to check it out. I noticed that my crank arms were pretty loose and decided to walk the bike home. Once I got home I noticed that the 8mm bolt running through my external bottom bracket was lose. I remember tightening it only a couple days ago though.

Does anyone know what may have caused my BB/ Cranks to loosen on their own?

I have an external bottom bracket with Raceface Cranks.

Figure B shows the bolt that came lose to a point where there was no resistance. I ended up tightening that bolt back up, but if I tighten it too much, the cranks start to resist on their own.

Figure A shows the two points where my cranks began to wiggle.

Any help or suggestions would be greatly appreciated.