I've got a 910xt and I was having issues with garmin express giving me the "We're Sorry..." message when I opened it and tried to log in. I discovered that it was my time being off which was causing that issue, but not after uninstalling/reinstalling express.
What's happened now is that the several activities on my 910xt which occurred between the last successful synch and the reinstall are still on my watch, but won't sync via express to garmin. I also can't do a manual upload from garmin connect because it doesn't show me any of the files on my watch since march.
Thanks