There are different versions of the liquid crystal library. Unfortunately many have the same name. I think that you may have a different version of the liquid crystal library than the sketch was written for. You will need to figure out which library the sketch was written for and install it, after deleting the wrong one. Or replace the library with a different one. I prefer the HD44780 library for my LCDs. Features automatic address and pin map detection. It would be easy to replace the existing library with the HD44780 one.