Does anyone know what is causing this?

    PLEASE CAN ANYONE OFFER ADVICE (OR PREFERABLY A FIX) FOR THE FOLLOWING ERROR, PLEASE?




    Fatal error: Invalid SQL: SELECT DISTINCT post.userID AS
    ownPosts,thread_visit.lastVisitTime,IF(thread_subscription.userID IS NOT
    NULL, 1, 0) AS subscribed, thread.* FROM wbb1_1_thread thread LEFT JOIN
    wbb1_1_post post ON (post.threadID = thread.threadID AND post.userID =
    42) LEFT JOIN wbb1_1_thread_visit thread_visit ON (thread_visit.threadID
    = thread.threadID AND thread_visit.userID = 42) LEFT JOIN
    wbb1_1_thread_subscription thread_subscription ON
    (thread_subscription.userID = 42 AND thread_subscription.threadID =
    thread.threadID) WHERE thread.threadID IN
    (18714,18713,18717,18657,18659,18072,18662,18019,18649,18588,18541,18575,18466,18507,18459,18444,18451,18452,18443,18326)
    ORDER BY thread.isAnnouncement DESC, thread.isSticky DESC,
    thread.lastPostTime DESC
    You get more information about the problem in our knowledge base: http://www.woltlab.com/help/?code=126
    Information:
    error message: Invalid SQL: SELECT DISTINCT post.userID AS
    ownPosts,thread_visit.lastVisitTime,IF(thread_subscription.userID IS NOT
    NULL, 1, 0) AS subscribed, thread.* FROM wbb1_1_thread thread LEFT JOIN
    wbb1_1_post post ON (post.threadID = thread.threadID AND post.userID =
    42) LEFT JOIN wbb1_1_thread_visit thread_visit ON (thread_visit.threadID
    = thread.threadID AND thread_visit.userID = 42) LEFT JOIN
    wbb1_1_thread_subscription thread_subscription ON
    (thread_subscription.userID = 42 AND thread_subscription.threadID =
    thread.threadID) WHERE thread.threadID IN
    (18714,18713,18717,18657,18659,18072,18662,18019,18649,18588,18541,18575,18466,18507,18459,18444,18451,18452,18443,18326)
    ORDER BY thread.isAnnouncement DESC, thread.isSticky DESC,
    thread.lastPostTime DESC
    error code: 126
    sql type: MySQLDatabase
    sql error: Incorrect key file for table '/var/tmp/#sql_333_5.MYI'; try to repair it
    sql error number: 126
    sql version:
    file: /homepages/44/d311830192/htdocs/forums/wcf/lib/system/database/MySQLDatabase.class.php (118)
    php version: 5.5.26
    wcf version: 1.1.10 pl 2 (Tempest)
    date: Thu, 13 Aug 2015 15:55:33 +0000
    request: /forums/index.php?page=Board&boardID=15
    referer: http://www.allbordercollies.com/forums/index.php?page=Index
    Stacktrace:
    #0
    /homepages/44/d311830192/htdocs/forums/lib/data/thread/ThreadList.class.php(110):
    MySQLDatabase->sendQuery('SELECT\t\tDISTINC...')
    #1 /homepages/44/d311830192/htdocs/forums/lib/data/thread/BoardThreadList.class.php(153): ThreadList->readThreads()
    #2 /homepages/44/d311830192/htdocs/forums/lib/page/BoardPage.class.php(163): BoardThreadList->readThreads()
    #3 /homepages/44/d311830192/htdocs/forums/wcf/lib/page/AbstractPage.class.php(90): BoardPage->readData()
    #4 /homepages/44/d311830192/htdocs/forums/wcf/lib/page/AbstractPage.class.php(46): AbstractPage->show()
    #5 /homepages/44/d311830192/htdocs/forums/wcf/lib/util/RequestHandler.class.php(64): AbstractPage->__construct()
    #6
    /homepages/44/d311830192/htdocs/forums/wcf/lib/util/RequestHandler.class.php(92):
    RequestHandler->__construct('Board', Array, 'page')
    #7 /homepages/44/d311830192/htdocs/forums/index.php(8): RequestHandler::handle(Array)
    #8 {main}