The true is this happen for a lot of things, but this guide will help a lot of users.

1. Boot from the rBoot CD
2. While hovering over the OSX partition, type in mach_kernel  rd=disk0s2
3. OSX started up fine, and then to avoid the need of keeping the rBoot disc in 24/7 to get into OSX, simply reinstall Chameleon.

:)