My Drupal 5 site suddenly started producing this error message:

user warning: Can't create/write to file '/var/tmp/mysql/#sql_21be_0.MYI' (Errcode: 2) query: SELECT DISTINCT b.* FROM blocks b LEFT JOIN blocks_roles r ON b.module = r.module AND b.delta = r.delta WHERE b.theme = 'CSL_theme_B' AND b.status = 1 AND (r.rid IN (2,3) OR r.rid IS NULL) ORDER BY b.region, b.weight, b.module in /home/cslorg/public_html/includes/database.mysql.inc on line 167.

I took the site offline, but the offline page still shows this before the standard offline text:

user warning: Can't create/write to file '/var/tmp/mysql/#sql_21be_0.MYI' (Errcode: 2) query: SELECT t.* FROM term_node r INNER JOIN term_data t ON r.tid = t.tid INNER JOIN vocabulary v ON t.vid = v.vid WHERE r.nid = 258 ORDER BY v.weight, t.weight, t.name in /home/cslorg/public_html/includes/database.mysql.inc on line 167.

Any suggestions on what I should do to fix this? I googled it but didn't find this error message.