I have a stihl ms 290 chainsaw. I was cutting an old log today and chain seized up. Thought chain brake activated but didnt. I took the bar and chain off, put it back on, ajusted chain tightener screw- chain still frozen. I played with it a couple times (i always get it after at least few times) but no luck. And it happened when cutting so something is wrong. I have been having to tighten chain more often and taking longer to get chain on chain sprocket and tightened properly. Im thinking its the chain sprocket- I checked everything else. Any Ideas?