ERROR 305
The NEM Infrastructure Server (NIS) is not available. Try to restart the NEM software. If you are using a remote NIS, check your configured host for typing errors or use another remote NIS.
as soon as i turn back to default port, nis turns available...
Well, this is because your NIS booted with the default port. Now you're trying to connect to a different port but nothing's there. If you want to boot NIS with a port other than default, you have to change the config file @ path-to-nem/nis/config.properties. You'll find nem.httpPort = 7890 and nem.httpsPort = 7891 in that file. Change the values, then restart NIS.
BUT you probably wanted to change the port of NCC, did you? head over to path-to-nem/ncc/config.properties, change nem.httpPort = 8989 and nem.httpsPort = 9090 to the port(s) you wish to use & reboot the NEM software.
OR to simply restrict outside access to port 8989, do as amytheplanarshift suggested above, block the port.
@ciappa: Entschuldige, falls das verwirrend wirkt. Wenn du lediglich nicht möchtest, dass jemand "von außen" dein NCC aufrufen kann, dann blockiere via Firewall den Port 8989 (der Port über den der Nem-Community-Client standardmäßig läuft).