I try to install Mountain Lion and I can't. It says "This disk cannot be used to start up your computer"

I got the same error and just decided to format the HDD on a white macbook. Installation is running smoothly now. No need to re-partition (but of course I lost everything that was on the disk, so this may not be the best route for everyone).

Problem occurred for me on a machine with Macintosh HD partitioned in two - system area & user area.

An fsck initially indicated minor volume header information needed repair. I thought that might be the fix but no.....

I went through the list of fix possibilities from least to most complex and it wasn't until I followed souloxide's suggestion of creating an extra partition that I was able to get 10.7/10.8 installer to recognize the Macintosh HD partition as an install destination.

There's obviously a flag or two buried in the file system that are difficult to reset!

External HD disk partitoning works differently does it not?

Why are you replying to a year old post?

Allan