Cannot communicate with VEX Cortex SlaveCPU

When compiling code to our robot we get the following error: “Cannot communicate with VEX Cortex SlaveCPU. Master CPU communication is working.
Things I have tried:**
-Manually updating firmware on controller+cortex
-Updating VEXNet keys
-Using a serial cable
-Using a USB A to A cable
-Bootloading cortex+controller
-Using a different computer
-Manually updating RobotC
-Resetting the cortex with config button

This error is really stubborn! Any help would be greatly appreciated.

Usually this means the RobotC firmware is not loaded onto the cortex. Do a software inspection (robot menu->advanced) and post the results. cortex firmware should be at 4.25, and RobotC firmware at 1055 if you are using the latest version.