I took a break from playing Crusader Kings II for a few months. Since I've come back (November 2012), I'm suddenly unable to raise levies from most of my counties. The button is grayed out, even though there are some levies available to raise in the county. (The green/red bar for the levy in the county info screen is mostly green.) The most distressing part is that some of those counties could raise ships, and so now I have more troops than transport.
I tried raising all available troops from the Military screen, but most counties don't have any army on them. How did raising levies change?