Thanks, Ipstenu, yes I see that now.
Yes, keesiemeijer, I did all that. There weren't any mod_rewrite rules in my .htaccess file just the basic WP pretty permalink ones. I did all the deletion in numbers 5 and 6 above. The wp-super-cache folder doesn't exist in my plugins directory.
All my WordPress files are vanilla 3.1 now as I have deleted
define( 'WP_CACHE', true ); from wp-config.php
I'm not getting any error messages now, but when I activate Under Construction plug-in, when I get the following:
Notice: has_cap was called with an argument that is deprecated since version 2.0! Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /home/robcub2/iegoa.com/wp-includes/functions.php on line 3387
... which is really weird as I have it working with other installs of WP 3.1
And, when I activate the new, premium, version of WPML I get multiple error messages (see above) with my custom theme. But with 2010 and WPML, I get "The plugin generated 756 characters of unexpected output during activation. If you notice “headers already sent” messages, problems with syndication feeds or other issues, try deactivating or removing this plugin." .. and the plug-in doesn't work properly. (All plug-ins with my custom theme worked perfectly pre 3.1).
However, they're releasing another WPML upgrade on Monday. But their forum isn't besieged with people with the same problem so I really don't know what went wrong.
Thank a lot for your help, as always.