Web Site unaccessible, HTTP 500 error when accessing Theme Settings

Theme Editor Module and all other supporting modules (ctools, Views, Libraries) required are located at: sites\all\modules

When Theme Editor is enabled the normal site breaks, and can not be viewed at all (get a 500 server error). You can access the administrative console if you have a direct link to one of the pages.

With Theme Editor enabled, going into Appearance >> Settings >> Going into any Theme results in a 500 server error page.

With Theme Editor disabled neither of these problems occur.