Came on really slowly so not sure exactly when it started. Rest didn't really help much but eventually have found out its a postural muscle in the calf. Should be ok to keep running on it. Doesn't really hurt much running on it anyway, just comes on when I'm sitting down and running downhill.
01/2009 edit - ctretching best when foot pointed inwards.
not sure when it ended. Think at the time I thought about putting it had stopped in here but decided not to tempt fate.