Had exactly the same problem. This occured as I tried to install Ray's instant messaging plugin. The whole thing went pear shaped with the same error messages.

I noticed some improvement as I commented out (in the files mentioned) instructions referring to Ray's IM. The site came back up but there were still lots of error messages.

To solve it, I did a new install in a different sub domain. Went into inc/header.inc.php and asked it to point to my previous installation database, rather than see more the new empty database it had created. That's all ;)