It is almost certainly a problem with your subnet mask.
If your subnet mask is 255.255.255.0, then the .8.x and .9.x hosts are in different subnets, and the host must have a default gateway defines to describe to the host where to send "off-LAN" traffic.
If your subnet mask is 255.255.0.0 (this is the default map for this class), the both hosts are in the same subnet and should talk freely and without any default gateway needed.
If you have the router set one way, and the hosts another (i.e., router is 255.255.0.0 and the hosts 255.255.255.0) then traffic is making it one way (to the router) but because the router sees the traffic as existing in the same LAN, it does not route it (routers only route between different networks/subnetworks).
Check your subnet masks on all devices and verifiy they are the same, and if you are using 255.255.255.0, make sure all hosts also have the appropriate default gateway.
Good Luck
Scott
