Error: -69711 this operation couldn't proceed because the target's boot helper was mounted; you may want to try again I have a MacBook Pro 8,1 (13", 2011 unibody) running Yosemite (no upgrades). Tried to partition my SSD hard drive and it threw an error when it was almost through saying it can't find the partition.

I searched and found this fix (Can&#39;t create partition on free space with Disk Utility) successfully got to step 11, but when I try step 12 I get the error -69711. Does anyone have any suggestions, I'm stuck.
This happens when you've booted to the recovery system on-disk (CmdR) instead of using Internet Recovery (OptionCmdR). Since the local recovery partition is associated with the stack you're trying to resize, and that partition is mounted, diskutil refuses to perform the operation.

(This may only apply to FileVault 2–encrypted volumes, which require a working recovery partition to boot, but I don't have an unencrypted computer to check with.)