Another wireless MBL Time Machine issue

Here is a "dumb"thing to try. I had a similar issue with an AppleTV and seeing a wired iMac and wireless Win laptop. After an insane amount of troubleshooting, rebooting, and googling; the suggestion I found to fix it was to turn off IGMP, which is a protocol for multicasting, on the router. Look for such a setting on your router, disable the IGMP/multicast support and reboot. If it doesn’t fix it, oh well. If it does be happy and don’t ask why. ;o)