Ah, I didn't spot any of those posts previously; My bad. I can see your problem straight away though!
You're opening other tags outside the css-div tag, but then closing them inside it.
e.g. [FONT="blah"][COLOR="blah"][CSS-DIV="blah"]blah[/COLOR][/FONT][/CSS-DIV]
Here's the above code corrected:
[FONT="blah"][COLOR="blah"][CSS-DIV="blah"]blah[/CSS-DIV][/COLOR][/FONT]
I'd just use the font-family and font-size css properties instead of BBCode if I were you though, way cleaner.
also totally unrelated but if you're having trouble later about anything else regarding CSS there's a nifty little halp centrée for that kind of thing.