RT-N66U :: Administration - System non functional

Hi! I hit a very strange snag on my router .. no matter what port is used for
HTTPS Lan port and not matter what i try to modify (time server in my case)
i receive the message : This port had been used for HTTP LAN port.
It is very annoying as i cannot modify anything in Administration - System
Any idea about this?

Thanks!
Adrian

Operation Mode:Access Point(AP) mode
Firmware Version:3.0.0.4.354