The error seems to come from board3 portal (https://www.phpbb.com/customise/db/exte ... ortal_ext/
Support for that extension is in https://www.phpbb.com/customise/db/exte ... ortal_ext/
and from what I can see it's not made for 3.2 although with some tweaks it does work.
Use this in phpmyadmin in your browser
to disable all extensions in one go to get your board working again (with the portal disabled) until a solution is found. (read the file)
Should the script not function, you can use phpMyAdmin : look at the extensions table, find the record for the board 3 extension and set the field ext_active to 0. empty the /cache directory but for index.htm and .htaccess and your board should be up and running with the board3.
As always, take a backup (with phpMyAdmin) before attempting this.
: corrected to use the ext_disable in phpmyadmin .... that should have been .. in the browser