Q: Why is [an app] FC'g (Force Closing) all the time?
A: There is a fix. It is quite common that some apps (Market, Superuser, Camera) may need it and this fix is actually required for the ICS Google Music. Before I get to the fix, if Gmail or Facebook or something else that shouldn't be FC'g is FC'g - you need to wipe and re-flash.
The fix: Go to Settings > Applications > Manage applications > then either use the Downloaded tab for apps you would get from the Market (like Google Music) or All for system apps (like Superuser and Market) > find the misbehaving app and select it > select Force stop (if this is an option you can select) > (magic step) then hit Clear data (don't worry these apps either don't carry much data, or sync with the cloud, you won't be losing anything important) > you should be good, but a reboot wouldn't hurt > Enjoy!