This was happening to me last week, but only with one character. The server restarted that night, and when I logged in the next morning, it was fine.
I wish I could figure out what caused it, but I don't know. There were a few reports on the official support forums, with identical LUA errors (I had it too) when the map started not showing objectives. I think every person reporting it was doing quests in the Northern Barrens at the time, so it's possible it's related to a specific quest there.
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“All truths are easy to understand once they are discovered; the point is to discover them.†- Galileo