6607/6608 is a Mitsubishi Electric error code when adding/removing a controller.
There might be cases where Error codes 6607 / 6608 will appear, when CoolMasterNet/CloudBox is added (Removed) to (from) Mitsubishi Electric VRF system, on the wired remotes.
In some cases, the error will disappear by itself after a couple of minutes.
In cases that the error doesn't disappear, the solution is to power reset outdoors+indoors.
The issues are not electrical but logical. Mitsubishi units are sensitive to the disappearance devices connected to MNet after CoolMasterNet / CloudBox are connected.