IAX2 trunk suddenly does not work

hi, i have this wierd problem for 3 days now and i can not figure how to solve it. problem is:

we had IAX2 trunk setup between our two offices and they were always working great. but all on a sudden it stopped working without any clue of why. from the trixbox log of the RECEIVING END i can only see the following:

-- Accepting UNAUTHENTICATED call from 123.123.123.123:
> requested format = ulaw,
> requested prefs = (ulaw),
> actual format = ulaw,
> host prefs = (ulaw),
> priority = mine
== Connect attempt from '127.0.0.1' unable to authenticate
-- Accepting UNAUTHENTICATED call from 123.123.123.123:
> requested format = ulaw,
> requested prefs = (ulaw),
> actual format = ulaw,
> host prefs = (ulaw),
> priority = mine
== Parsing '/etc/asterisk/manager.conf': Found
== Parsing '/etc/asterisk/manager_additional.conf': Found
== Parsing '/etc/asterisk/manager_custom.conf': Found
== Manager 'admin' logged on from 127.0.0.1
== Manager 'admin' logged off from 127.0.0.1
== Parsing '/etc/asterisk/manager.conf': Found
== Parsing '/etc/asterisk/manager_additional.conf': Found
== Parsing '/etc/asterisk/manager_custom.conf': Found
== Manager 'admin' logged on from 127.0.0.1
== Manager 'admin' logged off from 127.0.0.1
== Connect attempt from '127.0.0.1' unable to authenticate
== Parsing '/etc/asterisk/manager.conf': Found
== Parsing '/etc/asterisk/manager_additional.conf': Found
== Parsing '/etc/asterisk/manager_custom.conf': Found
== Manager 'admin' logged on from 127.0.0.1
== Connect attempt from '127.0.0.1' unable to authenticate
-- Accepting UNAUTHENTICATED call from 123.123.123.123:
> requested format = ulaw,
> requested prefs = (ulaw),
> actual format = ulaw,
> host prefs = (ulaw),
> priority = mine

and then it hangs up. at first it looked like it was some codec issue...so i set up the codec (ulaw on both side as u can see) but it still did not solve the problem. any idea why?

regards,

khan