Windows Explorer can't see other subnet

We have a small network behind a Fortigate 30D.  At one time everything was on one subnet, but a few months ago a local network company made changes to our setup.  Now we have a lan with a few hard-wired virtual Windows servers on the 192.168.1.x subnet and a wifi subnet on the 192.168.11.x subnet.  We can ping and remote desktop across networks, but Windows Explorer can't navigate across.  I'm more comfortable working with databases than networks, but I would like to get this resolved if possible.  So - can someone point me to where I should start looking?