Thanks! I'm going to go out right now and check that out.
I'm back. You are a true gentleman and scholar, Ygransom! I jerked it back and, sure enough, it was loose. (I'm so glad I posted this question because I would have ridden tomorrow with the rack only locked in on one side and not seated fully on the right side. I found the latch on the left side. I just didn't see it before but I should have reasoned that it was similar to the locking one on the right side. I guess my brain was dead today. I unlatched the left side and took the rack off and could then clearly see the mechanisms. But the key still couldn't turn. I figured that maybe the latch had to be re-set so I installed the rack on the bike and pulled it back. Voila! The lever would now move properly and I could lock the rack on the bike. I think what happened is that while I was checking things out and unlocked the lock, I must have inadvertently pushed the rack forward and then tried to lock it without knowing that it wasn't fully back.
I mention this in case some other idiot runs into the same problem.
You guys are great!