Help !! "REF Mark C : incorrect spacing on HSCI 530 on GRUPPO PARPAS ELECTRA machine

Hey dear forum members

I have a problem on start-up during the machine when doing Reference to all Axis in Axis C (swivel head with A and B ) after exactly 25.77 mm it triggers EMG and shut down servo with "REF Mark C : incorrect spacing "
and after few start-ups (after turning down the power) it eventually get reference and the machine works normally including C axis .

Is there a way to determinate if the source of the problem is due to ruined REF mark on the encoder , or is it a potentially a mismatch with parameters that some of the personal working on the machine made?

just to clarify after the machine is done Ref at the start up with C axis , everything work normally and without problems in C axis .

and where is the parameter that indicates the distance C axis could move until it triggers the EMG ?

much appreciation to the helpers!