No, you should be able to get to any subnet on your LAN/WAN. Make sure you have a route via the inside interface of the PIX to the network that you are trying to reach on the Frame relay network using your inside router as the gateway.
Example:
10.1.1.0/24 Inside Lan
10.1.2.0/24 Network on Frame relay
Pix inside interface 10.1.1.1
e0 interface of router 10.1.1.2
Add to Pix
route inside 10.1.2.0 255.255.255.0 10.1.1.2
HTH
RJ