Hello ValleyCityPlat... and welcome,
What is the IP address of the device that your are trying to port forward port 515 for?
You can only port forward ports of a device that is using any of the SMC Gateway DHCP IP addresses.
Look forward to hearin from you.
If you are using a FireWall (FW) device, then you should have one static IP address that your FW Wan network interface should be programmed to. If you are using the Comcast Gateways (CG) internal DHCP server, then you will have real difficulty with using 10.1.10.10 is this is within the range of dynamic IP addressed being doled out. I would advide you to change your FW address to 10.1.10.5 and also change the CG DHCP Leasetime=Forever. This should work for you and you should be able to port forward that port to the 10.1.10.5 IP.
Hope this helps you out.