The CSS keys are what AnyDVD does wheen removing copy protection.
Under the CSS Keys tab if you keep this checked it will remember that it checked that DVD and will revert back to the saved key.
I would suggest you uncheck that box because for some rare reason AnyDVD did not remove the copy protection from a particular DVD correctly, it will use that remembered key to use as a source. If there was a mistake, it will occur again. It only takes a short time for AnyDVD to do it's thing so it's best to leave unchecked to avoid any problems.
If you have any questions about functions in AnyDVD, merely right click on what you are doubtful of, an explanation should appear for you.