Unable to boot iOS 8 Simulator
Solution 1:
The main cause of this error is that DYLD_INSERT_LIBRARIES is set. I suggest you unset DYLD_INSERT_LIBRARIES (likely in /etc/launchd.conf) or otherwise uninstall the product that set it, and then reboot.
OS X Yosemite has a software change to deal with this situation, so if you need the product that was setting DYLD_INSERT_LIBRARIES, I suggest you update to OS X Yosemite for your development.