What exactly is wrong here? Info or advice appreciated.

Hi all,

Can someone give me an idea of what's going on here? This is a 100% crop of a picture from today. (I'm not claiming that this is great art; I wanted to pick a photo that showed my problem.)

Is this chromatic aberration? Camera-motion blur? Subject-motion blur? Bad focus? I get this phenomenon A LOT on my Canon 17-55 2.8 IS with my T1i, and I have to say it bugs me. Pics from today with less backlighting and higher shutter speeds showed less of a problem. (I know there's SOME subject-motion here in, e.g., the hands.)

If it's chromatic aberration or purple fringe, how can I deal with it? I use Aperture 3.2.1 and Photoshop Elements 10.

Thanks a million for any insight or advice!