As above really - a 2860N has been running fine for months and then we connect a 2nd (using V120) line within hours its freezes up.
We have also replaced with another 2860n that does exactly the same both on same firmware 3.7.4.3 and used the .rst before config
Router runs fine when WAN2 disconnected

Any ideas?

what do you mean by freezing? the menus with the 2860 not responding? or just the adsl part?

The whole thing - you cant manage it, ping it, route via it. its totally non responsive

Is difficult two 2860's having same issue ... unless you did not use the *rst* for a clean installation ... or ...
the line has problems ... did you checked with the isp?
Also are you aware about some issues with the vigor 120 v2, if this causing the problem?
http://www.forum.draytek.co.uk/viewtopic.php?f=12&t=19429

There was another issue (can find the post right now in here) that after about 6 months some 120 will fail perhaps to overheat and may this is the problem IF your line is ok

Note i not saying there issue with your 120 but just if you feel to investigate it

the rst was definitely used and then the config restored - I had to be restored as its part of a Hospice network and would have taken hours to re-add from scratch.
The new 120 seems going in seems to be the only factor as the 2860 has been fine whilst is disconnected.

Draytek want the syslog, the sys ver dbg and sys qrybuf so I will get them and see what they say next.

its been up 3 days solid now without WAN2 connected to the 120 modem.

Now waiting to hear back from support.