For what it's worth, I firmly believe that Multibit's way of storing passwords is corrupt. Once I recovered my friend's password, he told me it was based on the password he had used but had some unreadable characters in it (the kind you can't type on your keyboard). Even when pasting the password from my software into Multibit's GUI, it kept saying it was the wrong password. I had to do it a whole different way through scripts, openssl, CUDA...

Anyways, you'll see me posting here and there about this topic. I do hope people can save time at the very least not trying to input the password in the GUI until their fingers are bleeding. It took me 4 months trying out 3 different methods and the one that ended up working is now scalable and easy now for me to deploy.

If anyone here is based in France or wants to chat about this, I'm open. Those like me based in France: we can even have a call.
It's not my job but I did it once and think I can do it twice, at least with this specific version. Good luck otherwise

EDIT: if you don't want to get technical and you don't need too much help, you can first try by following Multibit's own (deprecated) suggestions here https://github.com/Multibit-Legacy/multibit

Cheers!