I keep having the same problem. I took it to a dealer last year (got charged labor) and now the same thing is happening again.
Love the mower size, but I've had nothing but trouble with it from day one. First the steering, then the chain coming off, then the one front wheel staying turned while the other one is straight, now the chain again.
Wish they would come get it and give me my money back so i could get a better "working right" mower.