Mitsubishi Electric MELFA FR CR800 Series User Manual page 636

When Communication Server 2 is light blue or blue. (RS-232)
(3)
If Communication Server 2 is displayed in light blue with communication with the robot controller set to
RS-232, check the following.
Check item or cause
Is anti-virus software running virus checks
on RS-232 communication?
When a computer starts up, sometimes this
generates noise.
This noise can cause a communication error
in the robot controller.
27-636
Switch off virus checking for RS-232.
Either start the computer before connecting the cable or
start the computer before starting the robot controller.
Solution
27-636