Andy,
I have had to turn the Fritz!Box's firewall off to make it work in some installations, so try that. You really
don't need it if you are using NAT (DCHP) and if the PC's have personal firewalls. I am not sure why some
of the Fritz!Boxes work with and some not, just one of the mysteries in life.
Let me know if that solved the problem. If not, we can go to Plan B.
73,
Mitch DJ0QN / K7DX