Had a brain lock.
Still follow the migration guide
But you probably have wwwthreads at that version. which is a predecessor to UBBthreads.
It is structured entirely different.
So the test script is really written for the UBB 7.x versions
After 6.4.1 is working
If you have access to 6.5.5.
Then follow the upgrade guide.as much as you can.
Copying over the specified 6.4.1 files with 6.5.5 and run install/upgrade.php not install.php.

When and if you decide to upgrade to the 7.x versions you will need to run a importer.
ubbthreads_6_5_import
Which current versions and importers are in the members area.
So if it is in fact wwwthreads I would suggest that you do not go above php5.3
It is so old I can't recall what version it supported.

But I do know with early 7.x versions they all ran on php5.4-6 but they would not install properly on above php5.3

Good luck

Last edited by Ruben; 07/21/2020 1:40 PM. Reason: Added Comment

Blue Man Group
There is no such thing as stupid questions. Just stupid answers