Warning: Please be sure you have a good idea of what exactly is happening before following any advice that I write here. This may be risky! Please do a bit more Googling before pressing ENTER on a Linux terminal. :)

I had this same problem after I removed a partition containing Windows 7 using Disk Utility. The problem in my case was that the Windows 7 partition was removed, but the Windows boot loader installed on the Master Boot Record (often denoted MBR) remained. To remove it, use dd as in the example below.

EXAMPLE: If your Windows boot loader is installed on the MBR of your sda drive, from a Linux terminal run: (WARNING, DON'T BLINDLY TYPE THIS WITHOUT READING THE DESCRIPTION ABOVE:) sudo dd if=/dev/zero of=/dev/sda bs=440 count=1

The dd command is also helpful if you have an extra GRUB boot loader installed somewhere. For example, I mistakenly installed a GRUB boot loader on my second hard drive both in the second hard drive's MBR and in the second hard drive's first partition. rEFIt listed both of the boot loaders, even though only the one installed on the second hard drive's MBR worked. So to remove the extra GRUB boot loader on the first partition of the second drive I also used dd as below.

EXAMPLE 2: If you have an extra GRUB boot loader installed on a partition, in this example partition sdb1, from a Linux terminal run dd as in the example below. (Notice the "of=..." changed and the "bs=..." changed from the first example.) (WARNING, DON'T BLINDLY TYPE THIS WITHOUT READING THE DESCRIPTION ABOVE:) sudo dd if=/dev/zero of=/dev/sdb1 bs=446 count=1

I know this is an old question, but it was never really answered. I hope this helps many people who were led to this page while searching for this problem. God bless!

Same thing happened to me on Windows 10. In my case the enable bitlocker process changed the type code on my OSX partition. To verify and fix on windows, use gdisk. http://sourceforge.net/projects/gptfdisk/

Verification

• Open Administrative Command Prompt and run gdisk64.exe (assuming x64).
• "0:" which is a special syntax to describe disks in windows. (I only have one harddrive and 0: is the first)
• "p" to print the partition table

Type device filename, or press <Enter> to exit: 0:
Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Command (? for help): p
Disk 0:: 977105060 sectors, 465.9 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): FDABFC64-BD61-4C2D-95CC-AB54D6A16DAA
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 977105026
Partitions will be aligned on 8-sector boundaries
Total free space is 4028 sectors (2.0 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1              40          409639   200.0 MiB   EF00  EFI System Partition
   2          409640       293378375   139.7 GiB   0700  Customer
   3       293378376       294647911   619.9 MiB   AF00  Recovery HD
   4       294649856       976392292   325.1 GiB   0700  Basic data partition
   5       976394240       977104895   347.0 MiB   2700

In my case partition #2 is my OSX installation. Note that Code is 0700 which is incorrect (gdisk describes 0700 as "Microsoft basic data"). If you see the same thing proceed with the fix, if not stop here. Also, double check that your MBR is protective and not hybrid.

The Fix

Command (? for help): t
Partition number (1-5): 2
Current type is 'Apple HFS/HFS+'
Hex code or GUID (L to show codes, Enter = 700): AF00
Changed type of partition to 'Apple HFS/HFS+'

Command (? for help): v

No problems found. 4028 free sectors (2.0 MiB) available in 4
segments, the largest of which is 1947 (973.5 KiB) in size.

Command (? for help): w

• "t" is the command to change a partition's type code
• "2" is my OSX partition index (use yours)
• "AF00" is the type code for Apple HFS/HFS+
• "v" verifies the disk
• "w" writes the table to disk and exits