Sangoma phones not allowing access to Web page


I’ve a couple of new Sangoma s305 phones, one of which I’ve been able to access the web page for without a problem, but the other one wont allow me to access its web page. It seems to work in all other respects, but I just cant get to the advanced config.

Tried a factory reset and it still refuses to play. And now, the one I used to be able to access is doing the same thing!

Is there a known problem in this area, or have I got a duff batch of phones?