All fine so far.

When I place a call from the VoIP phone FreeSWITCH complains:

 [WARNING] switch_ivr.c:1941 switch_ivr_set_user() can't find user

   [default@192.168.14.10]

where 192.168.14.10 is the number assigned to the logical interface,

however the call goes through / everything seems to work.  

Somewhere in your dial plan, the set_user application is being called with
the above user and domain as parameter.

http://wiki.freeswitch.org/wiki/Misc._Dialplan_Tools_set_user

The logs should show you which extensions are being executed in the dial plan
so you can work out how it reached this point and why it's invoking set_user
there. Basically, work through the logic of your dial plan to find out why
this is happening.

I'm sure others will have more specific advice, but, basically, it has to do
with the details of how your dial plan is configured.