....... It is the same error I got yesterday evening and tried to solve. No idea how, but after some fiddling the "problem" seemed to have solved itself.
What did I fiddle?
- restarted webserver (maybe restart QNAP)
- cleared firefox caches
- tried another browser (Chrome) -> worked
- in firefox I tried
http://192.168.xxx.xxx/cops/login.html
And in the end it worked.
Maybe you should try?