upgrade to ubbthreads 6.5.5 then go to say ubbthreads 7.2
After that you should be able to upgrade to the current v7 version.
Just read the upgrade directions in the install folder at each step.
He is correct about one item , in the importer to goto ubb7.X has a include that requires
require ("../libs/mysql.inc.php");
require("../libs/html.inc.php");
require("../libs/bbcode.inc.php");
require ("../libs/ubbthreads.inc.php");
They all do not exist in the archive till ubb 7.3.0
As per Ruben's followup directions, upgrade from from 6.5.5 then to 7.3.0 then to 7.7.4 (most current release version today). Do not bother with versions 7.0.0 through 7.2.x
ubbthreads 6.5.5 (released May 31, 2006)
ubbthreads 7.3.0 (released May 7, 2008)
ubbthreads 7.7.4 (released March 7, 2020)
timeline source:https://www.ubbcentral.com/forums/credits.htmlEDIT:upgrade notes from 7.7.4 for the sake of keeping this "6.5.5 import path to 7.7.4" thread helpful to everyone who needs it:
March 1, 2020: the upgrade path is from 7.5.6 to 7.7.4 (most current release version)
https://www.ubbcentral.com/forums/ubbthreads.php/topics/263543/7-7-4-changelog-discussion#Post263543March 31, 2020: limited 7.0.0 to 7.7.4 testing was done, in an attempt to find and fix
installer/upgrader issues outlined here.
Additional notes from gizmo:iirc, the only bug is the global moderator permissions from 7.2.0 upgrading to 7.3.0
