I've seen the following message after saving a megamenu:
Warning : file_get_contents(sites/all/modules/md_megamenu/js/jquery.choosefont.js) [function.file-get-contents]: failed to open stream: No such file or directory in _locale_parse_js_file()(line 1488 in /XXXX/includes/locale.inc).
The file jquery.choosefont.js is indeed missing...
Please go to md_megamenu/js folder and change jquery.choosefont.min.js to jquery.choosefont.js
I'll update new version soon, sorry about this