1. Completely exit WoW. Go into your SavedVariables folder --
World of Warcraft > WTF > 123456#1 > SavedVariables, where
123456#1 is your account number -- and delete the
Bartender4.lua and
Bartender4.lua.bak files. If the problem was caused by files locked in a read-only state, the problem should now be resolved.
2. If you still have the problem, make sure you actually have the
latest version of Bartender4. Even if you think you already do, just delete it, redownload it, and reinstall it anyway. While you're at it, you may as well do the same for the rest of your addons. If you have a lot of addons, or are lazy, use the
Curse Client to automate the process.
3. If you still have the problem once all your addons are up to date, then you should consider the possibility that the problem is caused by another addon. To find out if this is the case, disable all addons except for Bartender4. Log in, change some settings, log out, and back in. If your settings are now saved, but get reset again when you re-enable the rest of your addons, then some other addon is breaking things.