[Vossi]

That means, that you are using the 'ANSI_X3.4-1968'-charset and that this charset does not support the htmlentities function.

Just try to open 'class_dm_vbglossar_entry.php' and check line 377, outsource

PHP Code:

# $popup = htmlentities($popup, ENT_COMPAT,  "$stylevar[charset]" ); 


by adding # at the beginning of the line.

You might find another part of the addon where this error appears; just do this again at the specific parts. That might fix this.