hg 1500 problem

i will start apologizing if i write down wrong, im brazilian, not an english expert.

I have 2 siemens

system version: HE580S.14.146

version n: 146.000

system version: HE580U.14.146

version n: 146.000

software build version: HI-G15.36.011

Operating mode: v3.0 ( 3013 )

they are in diferent cities interconnected via VPN established by another company.

the HG system with the only purpose of calling from one extension to another, so they can talk to each other and transfer any clients calls among head office and branch offices.

With this been said lets go to my problem. if from the head office i try to reach this branch office i listed, the call is established, the phone rings on the other side, but, when he pick up the phone there is no voice connection, i do not hear him, nor he hear me, and some seconds later the call ends on its own. If he tries to call me the same problem occurs.

What drives me crazy is that i have another branch office, with the same hipath 3500, same software, same version, all the same and it works perfectly.

can PLEASE someone help me, i dont know what else to do...