Aperture hangs during "Updating Mobile" shortly after starting

When I click on the iCloud icon in System Preferences window, "Loading iCloud..." is displayed at the top of the window, and the system basically locks up. The color disc is spining, and I cannot open other applications, force quit anything, or shutdown the system from the menu. I have to physically puch the button, and then restart the system.

I'm also having a problem with Aperture in which it locks up shortly after it opens, and it is showing "Updating Mobile." I cannot gracefully quit Aperture; I have to Force Quit it from within the Activity Monitor. I'm now wondering if these two situations are related, i.e., Aperture is okay, but the fact that I cannot open the iCloud Preference Pane is the same problem Aperture is having "Updating Mobile."

George