I read too quick too but was able to reinstall the "System Administrator" record by clicking + button at the lower left and renaming "untitled 1" to "System Administrator". I had to add a few missing records within "System Administrator" but after that, I followed the directions correctly and can now login as root.
Luckily I had backed up my image to an external drive before I clicked the wrong minus, so I just restored from that and verified that the OP's method does work to fix the root account login issue.
But since I am right in front of it here are the values of the original root account if it helps anyone else:
Real Name System Administrator
Apparently within the last hour 10.7.3 update came out. It has fixes for Directory Services, but doesn't list this particular issue. If I end up testing it out later on I'll report back on whether the root login still breaks or not.
I too would like to thank the OP for this thread.
I was stumped, and I took my MBA into the San Jose (Cupertino's closest) Genius Bar. All the Techs were stumped, and the lead "Genius" said "we've got corruption here", that I needed to erase and reinstall Lion.
I generally take such statements to mean the lead idiot is out of ideas.
The only thing corrupt was the overestimation of his own knowledge.
The OP's solution worked fine.
For some reason, probably because of a posting I put in a similar thread a few weeks ago, I just got this thread in my mailbox.
The thing that worked for me IN 10.7.2 was significantly safer and easier.
Log in with an Admin account
Type in (without quotes) "dsenableroot"
enter your admin account password
enter in a password for the Root account. (it does not have to be the same PW used previously)
Verify the new Root Password
Up to 10.7.2 that enabled Root to be used. When you are done, go to the Directory Utility / Edit and disable Root. If you need Root again after it was disabled, you can use the Directory Utility / Edit to re-enable. The fix survives log off, restart, cold start and even crashes.
I tried the "dsenableroot" in Terminal and it still allowed me to enable root using the process above. However,
after 10.7.3 it seems that going the Directory Utility / Edit route requires you to enter a new root password everytime you try to enable root. If that is the way Apple chose to "fix" the problem, it seems a lot more of a hack than an actual fix.