Fix juniper fierwall communicatiob between VPN tunnels

Hi, I have a Cisco Tandberg Codec C20 video conference system located in my LAN. All the required ports are configured properly and routed to my video confrence system, and I am able to call and receive video conference calls from 3rd parties. I have a problem to initiate a video conference call to two remote offices that are configured with a VPN with my office. Those two remote offices are able to call me and start a video conference call, but I am unable to call them. The error message I get when I try to call using H.323 is "cannot call", which is instantly. I did not yet try to use SIP. When branch offices dial to my IP address, I can accept the call and all is working well. I think the problem is with the configuration of the VPN between my branch office and the other offices. I have control of my firewall only. I need someone exprienced with Juniper firewalls and VPN to identify the problem and help me fix it. I will release the payment only after I will be able to call both offices in a video conference call. Thanks, Guy