Linux traceroute packets blocked, but not window packets

[junior_kakou]

Hello everyone;
i have set up a site to site vpn between our site A and site B with two mikrotik routers. the vpn works well. both sites can see each other. behind site A is a 3600 firewall and the pc's of both sites can see each other.
when i ping back and forth from a windows pc as well as a linux pc, the pings go through. a traceroute back and forth from a windows pc, we can reach the pc behind the firewall. But a traceroute from a linux PC can't reach the PC behind the firewall at site A. The packets don't get through the router.
To sum up:
a tracert from Site B on Windows reaches the PC behind Site A's firewall;
a traceroute from Site B on linux can't reach the pc behind Site A's firewall.

what could be the problem???
Thanks