6664
The longer you wait with updating XOOPS, the harder it will get
My suggestion would be to:
1) back up everything, incl. exporting the database tables
2) Try to update to 2.0.18.1
3) In case of problems, try to solve them, but be eventually prepared to be forced to have a fresh install of XOOPS, and then import the tables and all other information (e.g. pictures, videos, etc).
This might take some time, but at least you will have a fresh clean install.
But let's hope that the upgrade will work, so you don't have to go to step (3)