Thanks Emsi,
I could not access any part of the site online, frontend or wp-admin backend, without getting this error.
I did try to disable/rename the ftp folder by FTP but that just caused more errors.
I backed up the mysql database, archived all the files & mods.
Then I did a clean install to WP 3.0.3, reloaded mysql, upgraded and rebuilt it theme and plugins one at a time.
Neither the plugins or theme(s) caused any fault in this process and all is well again.
So, fixed, but could not trace (and did not have the ime) to find the true error.