Not unusual after a major OS update to have some force closings.
Try finding the Gallery app in your Settings/Apps/ list and clearing cache on it.
If that doesn't resolve the issue you MAY have to do a factory reset which isn't uncommon after an update. Yes you will have to backup your stuff like pictures, etc from the device because that would be lost in a factory reset.
Of course someone else may have a better suggestion but that is the most common things I can think of.