We've been on the surface of Mars with Curiosity for over 6 months, and nothing serious had gone wrong - until Tuesday night. We got part of our data down for planning on Wednesday - when I started my shift as Long Term Planner. Then we got errors. The science team continued with planning in case the problem was with the communications, e.g. the links getting data from Curiosity to us. The engineering team scrambled to figure out what was wrong. By the end of Wednesday, they realized that Curiosity had not gone to sleep for its nap. That is equivalent to the "spinning wheel of death" we all hate to see on our computer screens.
There is, of course, a JPL Press Release and National Geographic has a nice summary with more engineering explanations from Richard Cook (Project Manager) and Madgy Bareh (JPL Engineer). Madgy is leading the "tactical" recovery efforts, which includes getting all the necessary settings into RCE-B. There is also a team working to reconstruct what went wrong and whether or not RCE-A can be used in the future.
It's been a very stressful few days, but we still have a working rover on the red planet! (Actually 2 - Opportunity is still going strong, too).
I'm still on duty at Long Term Planner through Saturday. My main job right now is to help the science team regroup on our plans for the next few weeks. As one team member said, "It's time to brush off our patience."