Warning on dashboard: "illegal string offset 'type' in…"

Hi – A site that I am managing is giving me an error code randomly on some pages in my WordPress dashboard. It isn’t stopping me from editing or accessing anything in the dashboard, but I’d like to figure out what the issue is and stop this warning from appearing:

Warning: Illegal string offset 'type' in /home3/pmspstem/public_html/wp-content/themes/thesis_183/lib/admin/options_post.php on line 150

The site is: pdxstem.org. The theme I’m using is Thesis.

Thanks for any help you can give!