I suspect this is some kind of Parallels bug. Twice after updating Fedora 15 I have found it wouldn't boot, instead entering emergency mode, from which it was apparent that I had a working system but with only the root partition mounted. The first time I simply reinstalled, it happened again yesterday and I decided to keep the VM around so I could investigate the problem. The symptoms were odd, on logging into emergency mode I discovered that /boot and swap weren't mounted, as I could mount these manually that seemed not to be the basic problem. Also the forums weren't full of complaints and I suspect they might have been had Fedora had some kind of problem. I decided to look for a Parallels related issue. Looking at mounted partitions in emergency mode the Parallels shared partition was also not mounted, I commented out that line from /etc/fstab and rebooted. This time the system came up and did an SELinux rebuild and informed me that Parallels Tools needed updating. When all this was complete I checked /etc/fstab and was surprised to discover that the line in fstab was now uncommented. The VM now works normally. I don't know what went wrong but it is unacceptable that some kind of error mounting the Parallels shared partition renders the system unbootable. The Parallels Tools update also seems like some kind of smoking gun.