"Error while opening sound device"

I am using Audacity in my undergrad music technology course. Yesterday, suddenly, some students started getting an error message, “Error while opening sound device. Please check the output device settings and the project sample rate.” At first I thought it was because of a safety feature installed on the school’s computers, but now it has happened on a student’s personal laptop. What is causing this and how do I fix it?

This FAQ from the manual should help you: http://manual.audacityteam.org/o/man/faq_errors.html#sound_device