asterisk users - Oct 2008 - app transfer problem

I all, I'm trying to transfer a iax2 channel trought dialplan app
transfer to another extensions (IAX).
The variable TRANSFERSTATUS report SUCCESS but the call isn't trasfered.
I haven't other information, in console I see only hangup of a channel.

My scenario is 3 asterisk box connected with iax trunk, I talk from BOX1
to BOX2 and I want to transfer user on BOX2 to another user on BOX3.
After transfer command is executed on BOX1 (return SUCCESS) on other BOX
I don't see nothing. Only hangup.
There are some way to debug the transfer? 

Thanks Pasqu.