I tried installing OS X El Capitan over my OS Yosemite.
At restart, during the installation process, I got this message:
"A mismatch between the mbr and gpt partition maps is not supported."
I was left with restarting the Macbook, but I always get this error message at startup and I can no longer use OS X.
Note: I use bootcamp with Windows 10.
Found a solution that worked for me:
Yes. First, download gdisk (URL in the OP) and run the installer package. Then run gdisk from a terminal window and run the v (verify command). If verify indicates no problems, then you're good to go and can just type "q" to quit. However, if it shows something like this, then you have the problem:
sudo gdisk /dev/disk0
Command (? for help): v
Warning! Mismatched GPT and MBR partition! MBR partition 4, of type 0x07, has no corresponding GPT partition! You may continue, but this condition might cause data loss in the future!
Identified 1 problems!
Next, display the MBR partition table and make note of the start and end sectors for your BOOTCAMP partition. This should be partition 4 unless you've added additional partition(s), which is not officially supported by Boot Camp. It should show something like this:
Command (? for help): r
Recovery/transformation command (? for help): o
Disk size is 1953525168 sectors (931.5 GiB)
MBR disk identifier: 0x7C170CB2
MBR partitions:
Number Boot Start Sector End Sector Status Code
1 1 409639 primary 0xEE
2 409640 975693095 primary 0xAF
3 975693096 976962631 primary 0xAB
4 * 976963584 1952806911 primary 0x07
Next, display the GPT partition table information. Compare the start and end sectors for partition 4 to the MBR partition 4 start and end sectors. Most likely the start sectors will match, but the end sectors will be different.
Recovery/transformation command (? for help): m
Command (? for help): p
Number Start (sector) End (sector) Size Code Name
1 40 409639 200.0 MiB EF00 EFI System Partition
2 409640 975693095 465.1 GiB AF00 Customer
3 975693096 976962631 619.9 MiB AB00 Recovery HD
4 976963584 1953523711 465.7 GiB 0700 BOOTCAMP
Next, delete the GPT partition 4. (Note: this does not delete the actual partition from disk. It only deletes gdisk's in-memory representation of the GPT).
Command (? for help): d
Partition number (1-4): 4
Now, create a new partition 4 using the start and end sector values from the MBR partition 4.
Command (? for help): n
Partition number (4-128, default 4): 4
First sector (34-1953525134, default = 976962632) or {+-}size{KMGTP}: 976963584
Last sector (976963584-1953525134, default = 1953525134) or {+-}size{KMGTP}: 1952806911
Current type is 'Apple HFS/HFS+'
Hex code or GUID (L to show codes, Enter = AF00): 0700
Changed type of partition to 'Microsoft basic data'
Now, change the name of the new partition 4 to BOOTCAMP:
Command (? for help): c
Partition number (1-4): 4
Enter name: BOOTCAMP
Run the verify command. It should report no problems. If it still reports a problem, quit (q command) and start over.
Command (? for help): v
If everything checks out, write new partition table to disk and exit.
Command (? for help): w
Reboot and test your dual boot setup to verify all is working correctly.
