It’s a syntax error so you need to examine the line it’s referring to and check and correct the syntax php met an unexpected double quote mark and seems to be suggesting there ought to have been an ) closing parentheses. this is an extremely old post you have dragged up and I would expect this plugin/code to necessarily work given the version updates to BP since this was written.
btw editing core files in this manner is not advised really, if it’s a filter it ought to be written to a functions.php file living in a child theme
