Is it possible this problem is related to these errors in my server logs. Regardless, do I need to copy the highslide folder to the root directory?
File does not exist: /home/myserver/public_html/highslide/highslide.js
File does not exist: /home/myserver/public_html/highslide/graphics/zoomin.cur
EDIT: Because copying the highslide folder to the root seems to have fixed it