cyau….are u using WMPU 2.9.2 and Sitemap Generator V3.2.4..??
If yes,uninstalles it and then install the previous version,V3.2.3 manually…
Click here to download that version…
after install,please ignore the upgrade notification…
It’s happened to me before…and after I do this,I found that the last xml update was about a month a go,end of may,although I set cron twice a day…..
but now it’s fine…
Just wait till fully support for 3.0 multi-site… =)