Javascript error in admin front page

I tried today to login via browser to the admin page. After inputing the credentials, the admin page only shows the ReadyNas logo. This happens in Chrome (63) and Firefox (). Upon console inspection, I found the following errors:

1. ext-all.js Failed to load resource: net::ERR_EMPTY_RESPONSE

2. frontview_6.9.2.js:13 Uncaught TypeError: Cannot read property 'prototype' of undefined
at Object.extend (frontview_6.9.2.js:13)
at frontview_6.9.2.js:77

I can still login by using Edge. Anyone has any similar problem?

My firmware version is 6.9.1