Currently Being ModeratedFeb 9, 2013 4:35 AM (in response to lemonglass)
Error message free launch failure after an update can be due to an out of date Quicktime, iTunes 11 needs the latest QUicktime if it is installed.
But this doesn't sound like your problem, if you had to force quit your library may be damaged.
Does iTunes open in another account? That's an important step in troubleshooting..
But as a quick test you can try a shift key start.
Hold down the shift key and try to start iTunes. Keep holding the shift key for a while and you should get a prompt to choose or create a library. Assuming you get this far try creating a library away from your music folder, say in documents. This is just a test to see if iTunes will open, don't put any music in it. If your old library is damaged, we will have to deal with that separately.