lightning update error, solution and its issues

[adispi]

hi.
i am having issue with lightning (currently 1.0 but i had this issue a long time).
from time to time when you update a meeting we get an error and the connection to the calendar is broken until thunderbird restart.
(if you want a way to repreduce this error send an appointment request, mwke sure the other side approves, and on the reply press the update button and you will get this error.
our calendars are set as dav in the following way:
http://zimbraserver/dav/user/calendar

i have found that on login request to the calendar, if i put username@domain.com i no longer get those errors.

however, i just found out that while i do not get the error, i also do not get free/busy time any more.
if i go back to only username when authenticating to the server, free/busy is working but the error is returning.

anyone know what is the correct way here to make both work?

thank you.