1. What exploit are you attempting to use?
2. The target machine must be vulnerable to the exploit.
3. You need to make sure you have chosen the appropriate "Target" OS + SP. The memory mappings on SP2 and SP3 differ.
4. Are your target machines on the same subnet? Are your machines behind any firewalls? Try to telnet/netcat to the target port.
5. Is 192.168.1.6 your local IP? This should be your machine's IP if you are using reverse_tcp.