I have no multiple subnets. Network setup is very basic, default 192.168.0.1 for the gateway, 255.255.255.0 netmask, blah blah blah. Aside from a bit of port-forwarding, there's nothing really going on beyond the stock setup in this router. If there was, I would have mentioned it.
I could paste in a results file from SIW if you really think more system details will help...
Oh, and BTW, I've tried plugging an external USB drive into the SharePort - a NexStar USB-to-SATA case with a 1TB drive in it. SharePort DOES see that, detects it as a "Sunplus Technology Inc. USB to Serial-ATA bridge", and I can connect to it (after a router reboot), but it doesn't appear in Disk Management... I gather I'm running into the drive-size limitation reported by others? In any case, the utility does appear to be communicating with the router's USB port, it just doesn't seem to know what to do with the printer...