I've had this error five times now. I've redownloaded it three times, I've tried installing from DVD, USB, and internal HDD. It hangs on 90% for a few minutes then suddenly switches to "Your PC will restart in a few moments and hangs there for another few minutes before seeing this error. I'm using a Lenovo ThinkPad Edge E420s with Windows 7 Home Premium on the HDD and Ubuntu 11.10 on an mSATA SSD. Any ideas on how to fix this?
I would actually recommend you not follow an upgrade path, I have seen several people attempt it get further than where your problem is happening, and it still not working. The problems people have after the upgrade does succeed include (and are not limited to); no Metro apps installing or working, other strangeness.
If you've already messed up your Windows 7 install, research and or ask another question about how you can recover any important data out of the Windows 7 install.
Remember Windows 8 is still not 100% complete, and the upgrade path process appears to have not been tested in the wild / is still being worked on, and has not been recommended to take as part of testing Windows 8.
Instead you should either