I have an iMac 27 that can not boot up because of a panic(cpu 8 caller 0xffffff80237afbab). [ 05-23-2016 ] Had trouble starting up after what must have been an Apple OSX update, but not sure. I do know I had the computer on for a handful of days and not using it. Later I returned and discovered it shut down. I turned it on, then the grey Apple Icon screen appeared showing the progress bar... After a few minutes it froze about midway through. After another 30 minutes+ still the same. Shut down holding power button in... Then unplugged iMac waited 20 sec then plugged in. Waited 5 sec, then started. It did restart with no seen problems. Everything seemed fine. I worked in Mail, Safari, Firefox, Fireworks, and Photoshop for a few hours. Later I shut down my iMac 27 for the night. [ 05-24-2016 ] The next day on boot up received below error message : ------ START error message ------ panic(cpu 8 caller 0xffffff80237afbab): "userspace panic: assertion failed: 15E65: launched + 143824 [527954A7-A0F1-305E-B26A-7E63282CA0FB]: 0xffffffffffffffff"@/Library/Caches/com.apple.xbs/Sources/xnu-3248.40.104/bad/kern/kern_ Debugger called: <panic> Backtrace (CPU 0), Frame : Return Address 0xffffff83c7ae3d50 : 0xffffff80232dab12 0xffffff83c7ae3dd0 : 0xffffff80237afbab 0xffffff83c7ae3e90 : 0xffffff80237c0f05 0xffffff83c7ae3fb0 : 0xffffff8023827a1 0xffffff83c7ae3e90 : 0xffffff80233eca76 BSD process name corresponding to current thread: launched Mac OS version: 15E65 Kernel version: Darwin Kernel Version 15.4.0: Fri Feb 26 22:08:05 PST 2016; root:xnu-3248.40.184~3/RELEASE_X86_64 Kernel UUID: 4E7B4496-0B81-34E9-97AF-F316103B083 Kernel slide: 0x0000000023000000 Kernel text base: 0xffffff8023200000 __HIB text base: 0xffffff8023100000 System model name: iMac13,2 (Mac-FC02E91DDD3FA6A4) System uptime in nanoseconds: 50611869924 ------ END error message ------ I have tried zapping NVRAM, SMC, to no success. Also I have disconnected ALL USB devices, even 2nd monitor, to no avail. Not able to boot into safe mode. I am able to boot up in the Recovery Mode, and did run disk utility, found no errors. I have held up from doing anything else. Any help or thoughts on the cause of this issue will be most appreciated. Thanks!