I had the same problem. Here's what worked for me.
1. Verify that all computers appear on the network. One of mine did not show because the network sharing option had changed. I don't know why./
2. Remove the secondary computer from the grid (completely).
3. Add it back using the IP address not the computer name.
4. Shut down both computers. Not restart but shut down.
I then rebooted my router and started the computers and everything was fine.