Alfred 2 fails to launch after upgrade to Yosemite
Don't use Alfred myself so I can't give a specific answer.

Something I would try though is using opensnoop to see if I can work out where it is failing.

If you type sudo opensnoop | grep alfred into a Terminal it'll show you all the files that Alfred is touching. That might help you identify where it is crashing, for example if it is a corrupt plist file.