Create SDDL failed, Error: 1332
Well, I have found the problem.
I'm running Windows 7 in Spanish, so the right command is:
netsh http add urlacl url=https://Melnibone:443/ user=todos
Funny, isn't it?
UPDATE:
If you want, you can add a comment to this question telling us how it is in your language.
For me, this issue was caused because there was already an HTTP reservation for the address and port I was using when tried to add an HTTPS reservation.
I found out what was going on when I ran NETSH HTTP SHOW URLACL
and saw that the address was already reserved with a different protocol.