My dentist told me that stopping smoking has caused soreness & redness in the palate of my mouth. has been there for 1 month plus now is this common?

Hmmmmmm.: I'm not sure if i personally would agree with that observation. Smoking can and will cause changes to the soft tissues of your mouth, including the palate. I would think that over time, the tissues will revert back to their natural healthy state, unless there has been some irreversible damage. You might want to check with an oral surgeon regarding the health of the tissues of your palate.