I had the same issue today. I could not check in via the iphone app, then when I tried to check in via the website, I received a "Check-in Advisory" stating I needed to an agent's assistance.

I called the PM Desk, and the very helpful person said everything looked good. We almost ended the call, and I asked if he could check the upgrade list from MSP to SLC. He said do you mean DTW...then he looked and realized that the flight had changed from when it was originally booked (I was notified about a month ago, but my itinterary show the change).

After placing me on hold for a couple of minutes he came back stating the (change) ticket was not issued...weird! Anyway, a couple minutes later he confirmed my seats and my flights (everything as it was on my itint before I called) and after we hung up, I was able to login.

Probably not a stellar day for the IT department.