IE versions before version 9 do not support Array.indexOf as used in (e.g.) js/edit_entry.js.php line 45 (referring to mrbs-1.4.10). Please include a compatibility implementation of the function. You can find one on http://stackoverflow.com/a/3629211, and a more recent one on MDN (see "from MDC" link on that page).
[Personally I use recent versions of IE of course, if at all. But there are still users of IE8 out there, such as my client. Rather than trying to convince all of them or change all occurrences of this function in your code, providing the compatibility implementation seems easiest.]