"dyld: could not load inserted library '/usr/lib/libgmalloc.dylib' because image not found"
Disable "Enable guard Malloc" from diagnostics to run app in device.
This is because Xcode mount wrong DeveloperImage. If you open the Settings-> Developer you will see that the "Enable UIAutomation» and others are missing.
For fix:
- move all folders from "/Applications/Xcode6-Beta2.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport" except "8.0 (12A4297e)" to safe place
- reboot the phone
- connect your phone to xCode 6 beta 2
- restore folders in DeviceSupport
This is the only thing that helped me. Even re-flashing on ios8 beta2 does not helps.