The Go2wpForo plugin uses PHP Session. As far as I see, your hosting configuration is wrong, the PHP session path doesn't exist, or it's pointing to a wrong directory. You should contact to your hosting service and ask them to fix the PHP session path, to avoid such errors:

open(/var/cpanel/php/sessions/ea3/sess_b42b989264c987fc64148eb6189a656e, O_RDWR) 
failed: No such file or directory (2) in 

I'm having a go at migrating a phpBB forum to wpForo, as I find WP so much easier to keep up to date with new versions.

I've installed WP on a sub-domain, using the Wordpress Toolkit in CPanel.  I then installed other plugins , again in WP Toolkit.

Logging in to my site, all looks good.

Then I installed Go2wpForo 3.0.0.  I now see the following error: -

open(/var/cpanel/php/sessions/ea3/sess_b42b989264c987fc64148eb6189a656e, O_RDWR) failed: No such file or directory (2) in /home/pompeybb/public_html/wpforum/wp-content/plugins/go2wpforo/Main.php on line 60

Warning: session_start(): Failed to read session data: files (path: /var/cpanel/php/sessions/ea3) in /home/pompeybb/public_html/wpforum/wp-content/plugins/go2wpforo/Main.php on line 60