Here’s what worked for me;
1) Delete entire folder WP-Includes from my host
2) Download update of wordpress through wp site by going to Tools – Upgrade – Download 2.8.4
3) Open downloaded wp folder and upload the WP-Includes folder to the host
That’s it. All that is being done is the wp-includes folder is being replaced. First delete the folder, then download and upload another wp-includes folder.
Any errors resulting from the first upgrade should be resolved by downloading the folder again.
Very frustrating and took a number of hours to sort, just happy it’s resolved now.