Depends on your model of macbook as to whether you can use LW 5. Needs to be an intel 64-bit otherwise you are limited to using LW 4.

It's my guess your problem is with your original OSX installation and that Java is not working as it should. Over a year ago I had problems with LW 4.18 and 5 on one of my OSX installations but worked fine on same computer in a different OSX installation on a different drive (LW 4.16 worked fine.) Eventually LW 5 worked on the main OSX after 6 months however I'm not sure what the answer was such as a mac update or reinstalling java or reinstalling the osx from scratch (clean install).

Unfortunately on MacBook you only have one hard disk drive so you cannot experiment with a second OSX startup drive unless you partitioned your drive.