2.0.5 is quite very old.
On Launchpad.net, you can find 2.1.2 version, then, starting from 2.2, you can find releases from Github.
Starting from 2.2, the upgrade of database schema use sql scripts from file/updates : the upgrade.php execute que 7???.sql then update GUI_VERSION with 7???. So I strongly RECOMMAND procedure :
- stop Apache
- install OCS Inventory OcsReports
- execute sql scripts + update GUI_VERSION from current +1 up to last number of version you choose
- start Apache
(It's strange to install a new version and doing database upgrade later with web interface : the agent don't wait and could receive bad response from /ocsinventory service ...)
Back to your problem, there is no secure script to upgrade from '6008' (2.0.5) to '7006' (2.1.2). I suggest you create an instance with blank database for 2.1.2 and compare database schema and create you own sql script with create new tables and alter new columns + insert into config : quite difficult but I dit it.
The 2.2 version, then, can upgrade directly from 2.1.2 (7006 -> 7007+7008+7009).
(I dit it : 2.0.5 -> 2.4.1 and then -> 2.8.1, with a quite big database ~14000 rows in hardware and ~8 M of rows in software : be carefull with very long 7039.sql with this large table software !)