Database Errors, what caused?

[SVTCobraLTD]

post Check Warning: Table is marked as crashed

Database error in vBulletin 3.6.10:

Invalid SQL:
SELECT COUNT(*) AS count FROM post AS post WHERE dateline >= 1274127767;

MySQL Error : Table './XXXXXXXXXXXXXXXX/post' is marked as crashed and should be repaired
Error Number : 145
Date : Monday, May 17th 2010 @ 10:18:38 PM
Script : http://XXXXXXXXXXX.com/
Referrer :
IP Address :
Username :
Classname : vB_Database

Any idea's on this? Error happened for an hour.

--------------- Added [DATE]1274153161[/DATE] at [TIME]1274153161[/TIME] ---------------

Here is another received during the same time...

Database error in vBulletin 3.6.10:

Invalid SQL:

SELECT
IF(votenum >= 1, votenum, 0) AS votenum,
IF(votenum >= 1 AND votenum > 0, votetotal / votenum, 0) AS voteavg,
post.pagetext AS preview,
thread.threadid, thread.title AS threadtitle, thread.forumid, pollid, open, replycount, postusername, postuserid, thread.iconid AS threadiconid,
thread.lastpost, thread.lastposter, thread.lastpostid, thread.dateline, IF(views<=replycount, replycount+1, views) AS views, notes, thread.visible, sticky, votetotal, thread.attach,
hiddencount, deletedcount
, NOT ISNULL(subscribethread.subscribethreadid) AS issubscribed



, vbookie_item_id
FROM thread AS thread

LEFT JOIN subscribethread AS subscribethread ON(subscribethread.threadid = thread.threadid AND subscribethread.userid = 1049 AND canview = 1)

LEFT JOIN post AS post ON(post.postid = thread.firstpostid)



WHERE thread.threadid IN (0,12615,12430,12339,3101,10306,11184,9365,10942,5 226,7537,9280,10122,2674,8228,6631,7042,5161,6114, 5376,5140,4772,5027,4396,4386,3929,2752,2707,5,269 9)
ORDER BY sticky DESC, lastpost DESC;

MySQL Error : Table './xxxxxxxxxx/post' is marked as crashed and should be repaired
Error Number : 145
Date : Monday, May 17th 2010 @ 10:17:15 PM
Script : http://www..com/forums/forumdisplay.php?f=59
Referrer : http://www..com/forums/index.php
IP Address :
Username :
Classname : vB_Database