Ethernet connected:
Check if under Host in VisualCut the correct cutters IP address is entered.
Transmission errors are most of the time due to a network issue (assuming the cutter is connected through Ethernet)
Check if one gets a clear ping, How to ping
Consider for troubleshooting purposes a direct Ethernet connection between rip and cutter (requires an Ethernet crossover cable).
Try the USB connection (make sure to change the connection type in VisualCut to USB)
USB connected:
Make sure to use a USB cable shorter than 10ft. Longer cables could cause issues even if they worked before.
Configure VisualCut to either USB or Ethernet (based on the connection)
In case of a USB connected cutter, try a different USB port? Try with or without a powered USB hub.
Is the Summa visible under the under the Caldera Server Admin > Devices > USB Tab
Try using the Ethernet connection. Ethernet is preferred especially with longer rip to cutter connections.
Either Connection:
Check if cutter language is set to DM/PL (This is a setting on the cutter itself).
MENU -> SYSTEM SETUP -> EMULATE -> DM/PL