Stretch stretch stretch!
So I don't get it - had it once or twice, but see people with it all the time. There are loads of different stretches to do (check online) ... but it's funny to do because the band has no stretch receptors so you can't really feel when you're doing it right! Also stretch your hips too - this is where the ITB starts.
Failing that some hardcore massage can ease it out .. but I've seen people wincing from the hardcore massage (which then fixed them!)
Good luck fixing it ... and then if your prone to it ... stretch more