Same thing happened to me this week however it was with a practically new KMC chain. I run a Shimano 105 10 speed triple 50/39/30t and whilst cycling up hill I shifted gears and the chain stuck in between the 39 and 30 chain rings. I took a picture as I couldn't believe this could actually happen.
Thankfully I was near a garage and asked if they could help as even though I had a multi tool it didn't have a T30 torque head so that I could release the bolts. They totally helped and after saying a huge thanks and promising to bring my car in next time it needed a service I made my way home.
Upon checking on Strava I realised that my current 5703 triple chain rings installed as a full crankset in June 2015 had grinded out well over 15,400 kms to was probably due a change and the wear in the rings probably caused the problem. I usually change my KMC chain every 5,000 kms so I guess 3 chains for every crankset is about the limit. Thankfully I found a new 170mm crankset on Chain Reaction for just over £100. I will be installing this when it arrives as a precaution as I don't want this to happen again as I almost fell off into oncoming traffic when it got jammed.