I am same situation.
When I launch Simplify3d, the error message "Unable to connect to the activation server. Please ensure that you have an active internet connection prior to activating." But my Mac is connected to internet and I see internet sites. I tried 2 Macs (Mac Pro 2009 OSX10.11.6, Mac Book Air OSX10.10.5). The version of Simplify3d is 4.1.2.
When I tried on Windows 8.1 of Parallel desktop, Simplify3d on Win succeeded to connect to the activation server. But Simplify3d on Mac could not.