WordPress Database Error 28

Twice today I caught this error message in two blogs:

WordPress database error: [Got error 28 from table handler]
SELECT DISTINCT * FROM wp_posts WHERE 1=1 AND post_date_gmt < = '2006-03-03 00:31:59' AND (post_status = "publish") AND post_status != "attachment" GROUP BY wp_posts.ID ORDER BY post_date DESC LIMIT 0, 5

I saw this in MLQ3’s blog and in a co-worker’s blog. What’s going on?