Sorry if this was already stated above (I skimmed) but I thought I would give feedback while it was fresh:
I followed Yeahha's steps and they worked fine. I was re-locking the bootloader so that I can exchange for another Nexus. When the image file finished uploading, the phone automatically reboots. It takes about 3-5 minutes on the Samsung bootup screen before rebooting a 2nd time then ends on the activation screen.
At that point, to follow step 5, you have to first walk through the activation steps to get to the unlock screen. You can skip all the steps by just pressing "Next" through everything (no need to enter email or check/uncheck boxes, etc). Once you are in to the phone, you have to re-enable USB debugging in settings before proceeding.
After that Yeahha's steps are back on track and you are back to a like-new, unrooted and locked device. Thanks for the HOWTO. Can't wait to get the replacement and root again. Hopefully now that the SDK and drivers are installed, the next root wil go easier.