I had this same problem, and from reading through other postings on the forum I found the solution -- it has to do with using 1.5 (starting with sneakypeak, I think) without syncing to anything (I sync to ical but not to mobileme or an iphone). There's a wierd default state that doesn't work right if you're not syncing to anything.

I fixed it by going into preferences>sync and clicking reset. OF quit just fine after that.