After upgrading to Mobility Service a couple days ago, some users
suddenly can't sync mail on some of their devices. The problem device
will constantly prompt for a password, but then say it's incorrect (when
it definitely is not). Same user will have a second device that's
ticking along without a problem.

Not restricted to users with multiple devices, though - a few who have
only one device experienced the error.

I'm unfortunately pretty user-level, but will appreciate any tips on
what to look at & how to solve.