I purchased a refurbished (By factory) Poulan chain saw just a couple of days ago. I have had trouble with the chain coming off on several occasions. Most recently I engaged the chain brake and now it will not unengage. I managed to get the brake off the saw but am still not able to disengage it and because it is still engaged willl not go back onto the clutch. Should I be concerned since this is a new refurbished product or is this a common problem and if so how can I correct it. The bar length is 20"