OK, issue resolved!
It was most definitely a corrupt files issue.
After I download again the backup forum dir, files and db from the web host and ran the upgrade process on my dev server, it TOK (Tested OK)
Righto then, lets tackle the web host upgrade next.
Connect to the web host via FTP, ughh... stuck at "...retrieving directory...."
Seems the issue was exacerbated at the web host end as they needed to upgrade cPanel before I could connect via FTP.
Wait 30~40 mins for the that to finish.
Backup the forum database, again.
Then created a new user and db with the same credentials as the existing db via phpMyAdmin and imported the existing db to it.
Uploaded the complete 3.2.8 install package less /ext, /files and /image dirs
Then uploaded the old forum /ext, /files, /images /styles dirs and overwrote the config.php
Browsed to the /install dir and, voila, back online!
Completed the upgrade (database only), successful!
Check and tested the forum and the ACP and it all TOK!
Yeehaa and whew!
Ok now off for that well earned beverage