Ah there ya go always helps to put the proper path to the forum files in the integration settings.
Everyone gets hit by that one
Basically as the thread you link that solved your issue shows we can only supply the path that script is running on hense say
/var/www/html/gallery
so when it goes to forum integration settings it would suggest as thats all we can suggest since install is running on the above server path
/var/www/html/gallery/forums
If you correct the path to the right server path to the forums usually something like so everything is right as rain.
/var/www/html/forums