OS X Mountain Lion cannot be installed on "Macintosh HD"

What does your Disk Utility information say?

See this article:

http://www.macworld.com/article/1161588/troubleshoot_lion_install.html

As David showed in his link;

This should be your solution:

This disk is used for Time Machine backups

This message again means that the Lion installation will not successfully complete. The message can appear even though your startup drive is obviously not acting as a Time Machine backup. As covered in an Apple Support Communities thread, the likely cause is an errant Time Machine-related Backups.backupdb folder at the root level of your drive. This folder, created by and used by Time Machine, is fooling the Install app into thinking your startup drive is actually a Time Machine backup. The solution is to delete the folder.

@LynnQ:

how did you remove the backup folder?

How did you fixed it, i download Mountain Lion on my 2009 imac, when the computer restarted it said that Mountain Lion could not be installed that there was a problem with my HD. I had never had any problems with my HD. If i had known this i woulnt have downloaded Mountain Lion. Now i cant evern go back to Lion and recover my files. I have over 500gb of important iformation. Thanks Apple. What a dissapointment. Hope i can find a way to install Mountain Lion or at least get all my data.

Well, I just tried installing Mountain Lion over Lion 10.7.4 on a MacBookPro. I have the same problem (the installer claims my internal hard disk is being used by TimeMachine but I definitely do not have any folder named Backups.backupdb (or at least Spotlight cannot find it). I preformed many Spotlight searches and nothing with this or similar name can be found. (It's amazing and appaling that Apple made such an idiotic installer!)

I found the answer myself. The folder was there but for some reason was invisible. I managed to make it visible by holding the Option (Alt) key and selecting Browse Other Backup Disks from the Time Machine Menu. Somehow that made the folder visible and I was able to delete it. Now I can install Mountain Lion. This was really weird, phew.

I too am getting the "Mac OS X cannot be installed on OS X" message when I attempt to install Mountain Lion over Snow Leopard in my macbook pro with an Intel processor. My hard drive format is Mac OS X Extended (journaled), with a GUID Partition Table.

As Apple suggests, I rebooted, opened disk utility, and attempted to resize the partition on which OS X is installed. I got the following error message:

"Partition failed with the error:

Could not modify partition map because filesystem verification failed"

Can someone please help. I hate the idea of having to pay a shop to do this.

A million thanks

You might want to consider starting a new discussion. Since this one is marked solved, less people are likely to look at it.

I have the same problem with Mountain Lion not installing. I also get the message the HD i selected which is the only drive I have is used by Time Machine. How do I find the folder you suggest removing. I looked under Spotlight and Find and it was not there. The computer is under AppleCare but so far they have not been able to help me. I keep getting the lower level techs.

Look on the hard drive level where System, Applications, Users, and Library are. It is usually there.