Quote - If you are running Norton software it may have declared 3D Commune a Spammer by accident and sent it to the Blocked Senders List. 

Excellent idea - although, I'm afraid in this department I'm totally ignorant.  In checking the Norton 360 Firewall Prevention Settings, the only ones I don't recognize which are blocked in the Traffic Rules area are the following:

Inbound Net BIOS
Inbound Net BIOS Name
EPMAP
UPnP Discovery
Web Services on Devices
LLMNR
Web Services Discovery
SSDP

Under Intrusion Prevention section, 3dcommune.com is not listed

Does this make sense - was I checking the correct area in Norton for the Blocked Senders List?