Trouble connecting w/ mosaic designer for Mac (v1.11.5)

There was some issue with El Cap and multicasting in Mosaic. You could try this...

Close Designer and find your active ethernet port assignment by going to the Apple Menu / About This Mac. Then click System Report and find Network in the list. Note the BSD Device Name for the port you are using to connect to Mosaic (i.e., I'm en4 for my Thunderbolt Ethernet and en0 for WiFi).

Open Terminal and paste in the following, changing out "en0" for whatever you found from above.

sudo route -nv add -net 230.0.0.0 -interface en4

You will then need to repeat the above command with the IP addresses below, replacing out "230.0.0.0"
230.0.3.1
230.0.3.3
230.0.3.4

This worked for a cohort of mine who was having the same problem you were.

-j

Thanks. That worked out.

That fix works but remember if you jostle the Thunderbolt and lose connection Mosaic will grey out and the computer will need to be restarted before you can upload.

That fix works but remember if you jostle the Thunderbolt and lose connection Mosaic will grey out and the computer will need to be restarted before you can upload.