WordPress database error (Errcode:13)??

One of my readers alerted me to the following error on two of my blogs (http://thegivinghands.org and http://theturtletalks.com). I did not do anything to the blogs since yesterday. I deactivated all plugins but the error persisted:

WordPress database error: [Can't create/write to file '/tmp/#sql_d0f_0.MYI' (Errcode: 13)]
SELECT t.*, tt.*, tr.object_id FROM wp_terms AS t INNER JOIN wp_term_taxonomy AS tt ON tt.term_id = t.term_id INNER JOIN wp_term_relationships AS tr ON tr.term_taxonomy_id = tt.term_taxonomy_id WHERE tt.taxonomy IN ('category', 'post_tag') AND tr.object_id IN (148, 147, 144) ORDER BY t.name ASC

Err.. What’s going on?