xwiki schema update failure

I've been running xwiki for ages and ages but suddenly it's gone down the pan! It was loading some pages and not others. So I restarted Tomcat and now it never starts: 11:29:26,386 ERROR http-80-Processor24 http://guanxi.uhi.ac.uk/xwiki/ bin/view/Main/WebHome XWikiHibernateStore:updateSchema:177 - Schema update for wiki xwiki 11:29:26,681 ERROR http-80-Processor24 http://guanxi.uhi.ac.uk/xwiki/ bin/view/Main/WebHome XWikiHibernateStore:updateSchema:240 - Failed updating schema: Got error 127 from table handler 11:29:36,548 WARN http-80-Processor24 http://guanxi.uhi.ac.uk/xwiki/ bin/view/Main/WebHome JDBCExceptionReporter:logExceptions:71 - SQL Error: 1030, SQLState: HY000 11:29:36,550 ERROR http-80-Processor24 http://guanxi.uhi.ac.uk/xwiki/ bin/view/Main/WebHome JDBCExceptionReporter:logExceptions:72 - Got error 127 from table handler is there any reason it would want to start updating a schema? thanks, Alistair