1030 - Got error 28 from storage engine

SELECT ArticleId, ArticleTypeId, pub_date FROM ( ( SELECT articleid AS ArticleId, articletypeid AS ArticleTypeId, headword AS sorter, p.pub_date FROM contributorarticleassociation caa INNER JOIN people p ON p.UID = caa.articleid WHERE contributiontypeid = 1 AND userid = '16190' AND articletypeid = 1 ) UNION ( SELECT articleid AS ArticleId, articletypeid AS ArticleTypeId, headword4 AS sorter, t.pub_date FROM contributorarticleassociation caa INNER JOIN topicsa t ON t.UID4 = caa.articleid WHERE contributiontypeid = 1 AND userid = '16190' AND articletypeid = 2 ) UNION ( SELECT articleid AS ArticleId, articletypeid AS ArticleTypeId, CONCAT(p.surname, ' ', p.forenames, ' ', w.headword2) AS sorter, w.pub_date FROM contributorarticleassociation caa INNER JOIN works w ON w.UID2 = caa.articleid INNER JOIN people p ON w.authoruid = p.UID WHERE contributiontypeid = 1 AND userid = '16190' AND articletypeid = 3 ) ) z ORDER BY sorter