After moving to Oracle Enterprise Manager Cloud Control 12c, one of the annoyances I soon discovered was this message "The page has expired. Click OK to continue". When you're not actively using the console, it doesn't take long before the message appears, which is especially annoying when you have the performance monitoring pages running in the background!
Make sure you set your env before or go to your oms home ex: cd /u00/oms12.0.3/oms/bin
[oracle@ bin]$ ./emctl set property -name oracle.sysman.eml.maxInactiveTime -value -1 -sysman_pwd <your sysman password>
Oracle Enterprise Manager Cloud Control 12c Release 3
Copyright (c) 1996, 2013 Oracle Corporation. All rights reserved.
Property oracle.sysman.eml.maxInactiveTime has been set to value -1 for all Management Servers
OMS restart is required to reflect the new property value
[oracle@ bin]$ ./emctl stop oms
Oracle Enterprise Manager Cloud Control 12c Release 3
Copyright (c) 1996, 2013 Oracle Corporation. All rights reserved.
Stopping WebTier...
WebTier Successfully Stopped
Stopping Oracle Management Server...
Oracle Management Server Successfully Stopped
Oracle Management Server is Down
oracle@ bin]$ ./emctl start oms
Oracle Enterprise Manager Cloud Control 12c Release 3
Copyright (c) 1996, 2013 Oracle Corporation. All rights reserved.
Starting Oracle Management Server...
Starting WebTier...
WebTier Successfully Started
Oracle Management Server Successfully Started
Oracle Management Server is Up
[oracle@ bin]$