Has this issue been addressed? Greg's mention of the "Add Store Code to URLs" is in fact causing this problem. When I turn this option to "No", I can use HelloThemes menu items and don't get the 404 error. However, this will leave my site giving 404 errors to all site visitors while I work on HelloSlide or other HelloTheme extension. I hope this issue can be fixed soon. For some reason, this error opens up by default every time I log in to my magento admin panel. Kind of annoying. Hope help is on the way!