I found that there seems to be a limit on the IP address for the roku/slingplayer connection to work. The slingplayer/roku interface appears to reject any IP addresses that are longer than 11 digits. Hence XXX.XXX.XX.XXX would work, XXX.XXX.XXX.XX would also work, but XXX.XXX.XXX.XXX would not work. Based on the IP address you described for the roku, the interface probably wont work. You can get around this with a couple of options:
1. Change your LAN IP address to use an 2 digit subnet, for example 192.168.12.XX
2. Assign a static IP to your roku so that it uses a 2 digit suffix, for example 192.168.129.13 (use your router for this step to ensure you dont assign an IP already in use)
Again this is based on my experience, so hope it helps.