Illegal String Offset on Fixer Theme

Hello If you can take a look at the site youll notice the error. I was editing the slider and when i save it, it just gave me this error. Any ideas?
Warning: Illegal string offset 'id' in /home/soft/public_html/toprecruitr.com/wp-content/themes/upfront/library/servers/class_upfront_presets_server.php

toprecruitr.com/

I really do not like the upfront editor. Would this theme work with Visual Composer?