Hey gang, it was a simple fix thanks to some quick searching on stackoverflow.
Looks like on line 19 of bbpress-new-ui/bbpress-new-ui.php you had:
if ($val['checkbox'] == 1) {
This was throwing the string offset warning beause $val is not an array because in the line before it you set:
$val = $val['checkbox']
So to fix it and correctly compare the value of $val just change line 19 to:
if ($val == 1) {
Changed it in my plugins -> editor (via the wordpress admin page) and everything works fine now.
Please update the plugin with this fix so everyone else can benefit from it. Thanks!