What is the solution of camera error flash to need to cool down?

There is a thermistor near the camera that detects the temperature. When the temperature is too hot, it signals to the CPU and you get the message.

Do you feel any excess heat around the camera?

You could have a defective camera module, which is pulling too much current and hence generating heat. It could also be a problem with the voltage regulator that supplies voltage/current to the camera.

The easiest thing to try is to disconnect the camera, first both of them then one at a time, to see if that solves your problem. You would then order a replacement camera.

If you still get the message without any cameras connected, then you probably have a logic board problem.