The page not found problem is likely due to an HTML error you have made while editing some of the HTML files.
As for the missing enroll button, I had this problem on ironwood.master too.
After investigation, I realised the enroll button was hidden by the box at the top of the course_about page
I solved this by editing the file courseware/course_about.html. Specifically, look at lines 114-116 and expand the box by including the style attribute "min-height" to the following classes "course-profile", intro-inner-wrapper" and "table". Expand the min-height to something like 20cm and then you should see the enroll button.