cutter squeal case emergency stop message

Hi i have a interact one mark 2 of 1994 vintage with a 2500B controller and have a problen when either 3D milling or pocketing when the cutter starts to squeal when for instance if pocketing milling the corners the spindle stops and i get a message on the screen saying emergency stop button has been pressed?
Has anyone else had this problem? if so what caused it.
any help would be much appreciated.
regards
mark