Just finished fixing my pack and tried uploading it, but I can't overwrite the old one on the portal. I've saved it with a slightly different name for now, but could someone who can please delete the old one? Cheers.
Regarding passwords, four random letters seems the best way to me. Nice and short, and easy to remember.
I've solved now all of your levels as well, a couple of my solutions look backroute-ish though.
I can send you my Lemmix demos, just give me your e-mail address. Neat levels, I confirm.
As for passwords, another simple method could be just taking the first 10 letters of the level titles, that way, if you remember the name, you can easily associate the password with it. However, one problem is, that it has to be made sure that no two levels have the same first 10 letters, and for levels with less than 10 letters, the spaces should be filled somehow.