Sorry if I wasn't clear (or maybe gave way too much information). I don't believe I have access to a 6.4.1 installer, so my initial approach was to try moving the public_html directory & the MySQL dump to a server and deploying it that way. I actually did this both on my production server as well as a local MAMP server running php 5.4.45. Nothing was merged on either site. They're all the original files and data and, since no installers were used, everything was configured by hand.
Although both of these sites seem to work on the frontend, I can't actually login to either one using the credentials from the live site. The strange thing is, the mysql dump is from the live site so I'm not sure what the issue is there. Regardless, I created yet another account with a fresh install of 6.5.5 and then I attempted to merge the data on that site — which obviously, was a bad idea.
As for the 6.5.5 approach you suggested, I can definitely try that. I do have a 6.5.5 installer, but didn't realize there was an upgrade script. So I will give that a shot. Thank you so much.
You still need to get 6.4.1 working correctly before you run the upgrade to 6.5.5
You can thank isaac for giving you some very important info on php versions versus UBB versions.
I had a similar problem a few years ago with a very old site, older than yours because it was classic.
Where I had to run it on my local machine to upgrade.
I was using wamp but could not find a downgrade that was old enough to work.
I ended up with a old archived download from xampp to get the server software old enough to run the forum.
Not sure what the os is on your local machine but if it is windows another issue is the tables get named in the wrong case.
So if you upload it to a linux server then you have to edit every table name in the proper case.
The install folder has always been recommended to delete the contents after the forum is running.
So it may be missing from your backup.
But it should not be needed at this point to just get 6.4.1 running.
Just the proper server software versions. to make the forum run properly
I feel your pain.