I umplugged and moved my iMac (2.16 GHz Intel iMac running 10.5.6) to another room. When I turned it on, I was locked out of both user accounts.
I am 100% certain that I entered the passwords correctly on both accounts, as I tried each multiple times.
After I restarted the computer from the login screen, my passwords worked.
What in the world could have happened to cause this? Is it likely to happen again? Should I have a Linux Live CD waiting just in case?