After Effects wouldn't play back my PNG sequence, giving the following error message: 'AEGP Plugin PNGIO Support: PNGIO library error: Unable to decode PNG file ( 5027 :: 12 ). After clearing the preferences and then finally uninstalling and reinstalling AE, it still wouldn't work. Now my AE crashes on launch, giving me the following alert: 'Last log message was: <140735281160960> <BEE_WorkQueue> <5> thread main stack size: 524288'. I don't believe my PNG sequence was corrupt in any way...and I don't understand why AE can't open now. I am on a MacBook Pro (2014), OS X Yosemite 10.10, 2.5 GHz Intel Core I7 processor, 16 GB 1600 MHz DDR3 Memory, Nvidia GeForce GT 750 M 2048 MB graphics card. Any help appreciated!
Apple fixed some big bugs in OSX 10.10 with the 10.10.5 update. Have you gotten that update yet?
What is the exact version number of AE you're using?
It also might be a weird permissions issue. There was a thread a while back where creating a new, administrator account allowed them to launch AE. Found it: Premiere and After Effects CC 2015 quit unexpectedly on launch