I had a user ask me about this error. He was using Version 18.104.22.1685 (the original release), so I suggested that he apply some updates or check for font problems. He did some digging and found that if her removed Windows Update KB3102429 the problem went away. That led me to this discussion on the same topic which nails down a font problem. Since XI is still widely used, and since this might affect other versions, I thought this might help someone else.
And thanks to Josh Pals, Controller at United Gear and Assembly, Inc., or sharing his find.