Tvheadend

Hello, I am running a 'headless' media server using mpd and tvheadend.
The TV s/w does everything it is supposed to do apart from showing
'live' TV. I am using the TVHeadEnd web interface. I can record without problems.
When I click on the 'Watch TV ' link, the screen 'box' comes up, I
select a channel but nothing is shown. The log shows nothing amiss:-
Jun 19 14:13:38.889 HTTP: 127.0.0.1: /stream/channelid/72 -- 401

The server is a Raspberry Pi running raspbian.
I am accessing via firefox browser port 9981 on a Ubuntu laptop.
Help much appreciated.

Further to this, when I left click on the TV 'screen' box, I get:-
'An error has occurred, Location not found'