I've not been able to access my e-upgrade summary for a week or so either. I tried again a few minutes ago and it still didn't work and so, I wondered if there are other ways.

I went into an itinerary through the itinerary viewing area, clicked on the MileagePlus button at the side and clicked "continue" to pop up a new window to MileagePlus, was forced to enter my password yet again and, when I tried e-upgrade summary, to my shock, it worked!

Maybe this convoluted method will work for others too?