Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 64)

Basic Control Operation
Chapter 2
2-40
After the cause of a machine or system message has been resolved, some
messages remain displayed on all screens until you clear them.
CAUTION: Not clearing the old messages from the screen can
prevent messages that are generated later from being displayed.
This occurs when the old resolved message has a higher priority
than the newly generated message. The new message is still
displayed on the message display screen as an active message,
but does not appear in the message area of other screens.
Active messages are cleared from the screen in this way:
Press the [CAN] key to clear the most recent active messages
individually.
Clear all active messages from the error message display screen by
pressing the
{CLEAR ACTIVE} softkey.
(softkey level 2)
ERROR
LOG
CLEAR
ACTIVE
Important: Clearing active messages does not correct the problem that
caused the error; it only clears the message from the active file.
2.9.1
Clearing Active Messages
{CLEAR ACTIVE}