Bizarre error caused by temporary SQL tables

When searching my site, http://www.wikijob.co.uk with the keywords "reasoning" or "verbal reasoning" it seems to result in a very nasty error, for example:

http://www.wikijob.co.uk/search/node/reasoning

The search seems to work fine for all other search terms.

I have pasted the errors below:

user warning: Table 'temp_search_sids' already exists query: CREATE TEMPORARY TABLE temp_search_sids SELECT i.type, i.sid, SUM(i.score * t.count) AS relevance, COUNT(*) AS matches FROM search_index i INNER JOIN search_total t ON i.word = t.word INNER JOIN node n ON n.nid = i.sid INNER JOIN users u ON n.uid = u.uid WHERE n.status = 1 AND (i.word = 'search' OR i.word = 'node' OR i.word = 'reason') AND i.type = 'node' GROUP BY i.type, i.sid HAVING COUNT(*) >= 1 in /data/sites/wikijoba/includes/database.mysql.inc on line 172.

user warning: Table 'temp_search_results' already exists query: CREATE TEMPORARY TABLE temp_search_results SELECT i.type, i.sid, 8 * (13.3951290003 * i.relevance) + 5 * POW(2, (GREATEST(n.created, n.changed, c.last_comment_timestamp) - 1218897321) * 6.43e-8) + 5 * (2.0 - 2.0 / (1.0 + c.comment_count * 0.0222222222222)) + 5 * (2.0 - 2.0 / (1.0 + nc.totalcount * 5.29016558218E-05)) AS score FROM temp_search_sids i INNER JOIN search_dataset d ON i.sid = d.sid AND i.type = d.type INNER JOIN node n ON n.nid = i.sid LEFT JOIN node_comment_statistics c ON c.nid = i.sid LEFT JOIN node_counter nc ON nc.nid = i.sid WHERE ((d.data LIKE '% search %' OR d.data LIKE '% node %' OR d.data LIKE '% reason %')) ORDER BY score DESC in /data/sites/wikijoba/includes/database.mysql.inc on line 172.

I have tried rebuilding the search index but this did not seem to help.

NB Search 404 module is enabled, which is what is producing the search results below the error.