Recently I mucked up my primary partition containing MacOSX. Thankfully I had a system backup of it stored on another partition on the same disk (thanks Time Machine!). I was able to successfully restore the partition by booting with my installation disc (iAtkos S3 V2 10.6.3, but you could use any), but I could not start the operating system. I kept getting a ‘boot0: error’ message. After some searching, I discovered the possible reason for the error was due to my MacOSX partition no longer being marked ‘active’ or ‘bootable’.
I tried using various tools like gparted (which actually caused me more troubled than it was worth) and diskutil from the MacOSX terminal available via the installation disk. Nothing seemed to work.
For what it’s worth at this point, if you used gparted to try to set the boot flag, or modify the partition in anyway, you may have to give up and re-install. I did this, and was not only unable to see my partition with the disk utility (it showed up as empty space) I could not do anything with it either. It just showed up empty and neither diskutil (via terminal) or Disk Utility were able to use it. I eventually had to delete all partitions except for my data partition (leaving the rest as empty space) and go back to Disk Utility again. I was then able to create a new partition using Disk Utility and restore my Time Machine backup to it.
You can read more about ‘gparted troubles‘ here for a better understanding.
In the end, the following steps solved my problem. I restored my MacOSX partition one last time and rebooted. Same error. I than booted from my MacOSX installation disc and used the ‘repair disk’ option in the Disk Utility. I noticed in the Disk Utility that it actually noted that it corrected my MacOSX boot issue. When complete, I rebooted my system one last time and was finally greeted with my MacOSX login screen. Success!
I caused myself this problem by installing the latest version of MyHack, without really knowing was I was doing. After installing it and rebooting, my system was far worse off than just ‘boot0: error’. Use MyHack if you know what you are doing.