Apple - How to resolve error: "Couldn't modify partition map because file system verification failed"?

OK, this isn't too bad. Reboot while holding Command ⌘-S to enter single user mode. When it gives you a prompt, type

fsck -fy

then press return. it will repair your disk. When it's done, type


and try partitioning again.

The solution ended up being to create a Lion install disk, boot from the disk, run disk utility repair on the drive and volume, then resize the partition. Easier than I thought it would be.

This solution worked for me after receiving the same error:

  • Shut down.
  • Start up holding down Command ⌘ + S. (This will boot you into Single User Mode.)
  • At the prompt, type in the command fsck -fy.
  • When that finishes, type reboot.
  • Try resizing again in Disk Utility.