1030 - Got error 28 from storage engine

SELECT u.forename, u.surname, c.profile, u.id AS contribid, caa.contributiontypeid, u.email, CASE i.full_name WHEN NULL THEN u.institution ELSE i.full_name END AS institution FROM works a INNER JOIN contributorarticleassociation caa ON a.UID2 = caa.articleid AND caa.articletypeid = 3 INNER JOIN users u ON caa.userid = u.id INNER JOIN contributors c ON u.id = c.userid LEFT JOIN institutions i ON i.institution_id = u.institution_id WHERE a.UID2 = 6994 AND caa.contributiontypeid = 1 ORDER BY u.surname, u.forename