In case it helps, I experienced this error using tagDiv’s Newspaper theme (7.2) on PHP 5.3.29 and WordPress version 4.5.3.
Further, the theme authors are also looking into this issue. They’ve recommended a temporary hack (around line 215) of the n9m-font-awesome-4.php file. That code is on pastebin.
Here’s the code snippet:
function walker_nav_menu_start_el( $item_output, $item, $depth, $args ){
if (is_array($item->classes)) {
$classes = preg_grep( '/^(fa)(-\S+)?$/i', $item->classes );
if( !empty( $classes ) ){
$item_output = $this->replace_item( $item_output, $classes );
}
}
return $item_output;
}