I'm following the instructions in "docs/UPGRADE".
Regarding a clean process, I choosed to install the "3. Full Package", preserving the old 'config.inc.php', 'public' folder and uploaded files directory.
Next step, "Upgrading the OCS database": as Windows Server is the operative system, I choosed the method via "2. Web" by running a web-based script to the update: changed "installed = On" to "installed = Off" in 'config.inc.php' file.
I also used a copy of the old database (PostgreSQL 8.3.5).
Opened a web browser to OCS site, acessed installation and upgrade page: "If you are upgrading an existing installation of OCS 2.x, click here to proceed.", then button "Upgrade Open Conference Systems".
It took a second to have this information:
"Errors occurred during installation:
A database error has occurred: ERROR: relation "paper_presenters" does not exist"
I also tried with a slight different approach by applying the recommended patches against OCS2.3.5 before the upgrading process. It solved other errors ocurred during installation, except this one as I said. I used patches for the following bug numbers: 6495, 6900, 7275, 7425, 7427, 8003, and 8119.
Any help? Many thanks!