In local network area is everything OK?

jimasek wrote

In local network area is everything OK?

yes, in local area everythings works perfect (entering 127.0.0.1, 192.168.0.1 (router address) or external ip). the problem is only when trying to connect over internet and when the port is other than 80. though other configured virtual ports work perfect too.

yes, local is ok. when i set Remote Management IP Address: 255.255.255.255, then locally i can access management using 127.0.0.1, my external ip or 192.168.0.1 (router) and no matter what port is, but over the internet i cannot access it (only when 80 port is assigned)

Have you rebooted the router after changing the management port? If you do, it can be a bug. (I don't think it will be fixed since V7 is discontinued long time ago.)

You can try a third-party firmware openwrt

http://wiki.openwrt.org/toh/tp-link/tl-wr841nd

There is a openwrt firmware for V7 in the above page.
http://downloads.openwrt.org/barrier_breaker/14.07/ar71xx/generic/openwrt-ar71xx-generic-tl-wr841nd-v7-squashfs-factory.bin

yes, it was rebooted after changing the port. i'm not sure 100%, but i think this worked well some time ago, probably before firmware upgrade. eventually i'll try the firmware that was released prior the current one