after 6.0rc12 upgrade: 501 not implemented

RouterOS General
1

Upgraded my RB750G to 6.0rc12 by uploading the .npk to the webinterface, and now the webinterface is bricked.
Images on the frontpage are broken, and when trying to login I get “Error 501 Not implemented”

Router functions still work, and I can still ssh to the device.
Any idea how to fix the webinterface?
routerboard-501notimplemented.png
routerboard-frontpage.png

2

After downgrading to 5.24 using ftp/ssh and then upgrading to 6.0rc12 again it does work.
Seems you cannot upgrade straight away from an old 4.x version.

3

please attempt re-installation of RouterOSvia Netinstall tool. This what you saw is remnant that is not anymore available in clean 6.x installation.