On your mac there is an application called Font book.
It has the option to Validate fonts. I suspect that you have multiple copies of the font. See if this repairs the problem.
Other ideas (after you’ve tried that) would be to trash the marquee settings…..
Try it in a new user (to see if it’s specific to your OSX user)
and gulp a full uninstall/reinstall of MC
Also, for the record, MC isn’t supported with 10.6.5, but I’m running it right (5.0.3.7) now and Marquee does work.
Best,
Jeff G