Not sure what to tell you... from that it looks like they are in two different directories...
I would guess your DOCUMENT_ROOT variable is messed up as it should point to the same directory as Joomla.
Only other thing I could think, assuming you can't modify the DOCUMENT_ROOT server variable, is to go into the plugin code and hack it so every place that looks for $_SERVER["DOCUMENT_ROOT"] sub out with $mosConfig_absolute_path or its equivalent "/home/zomer86/domains/hard-beats.nl/public_html"
if that path is not correct then sub in your correct path... Ver. 1.0.3 will have a way built-in to define an absolute path... just not in 1.0.2 though
I´m a complete noob both at joomla, community builder AND phpbb.
I installed phpbb in a subdomain. And joomla in my domain.
forum.sorocababynight.com and sorocababynight.com, respectivelly.
I get the SQL error, but I have no idea how to make sure they´re both installed in the same database. How could I correct it (if they´re in different databases)? Or should I reinstall phpbb (and hope I don´t miss where I choose the correct sql database)?