Upgrade to Yosemite failed - MBR and GPT don't match?

Solution 1:

This post explains the procedure. Now is probably a good time to make a backup. Then proceed at your own risk...

1. Get gdisk
2. In Terminal: sudo gdisk /dev/disk0
3. Press v to verify your MBR
4. Press r and then o to list the MBR partition table
5. Press m and then p to display the GPT partition table information
6. Compare the numbers for partition 4 from the MBR and GPT tables. The start numbers should match, but the end numbers will probably be off.
7. Press d to delete the GPT partition 4 (Bootcamp). "Note: this does not delete the actual partition from disk. It only deletes gdisk's in-memory representation of the GPT."
8. Press n to create a new partition 4 (Bootcamp) using the start and end sector values from the MBR partition 4
9. Change the name of the new partition 4 to BOOTCAMP
10. Press v to verify
11. If no errors occurred: press w to write the new partition table
12. If errors occurred: press q and try again
13. Reboot

The important part is step 7 where you sync your GPT and MBR. Note that some of the commands (e.g. disk0, partition 4) may be different in your case. Please adapt them accordingly.