There are many reason for the client offline status. Below are the some reason with resolution
1. Systems are in unmanage condition. https://www-secure.symantec.com/connect/downloads/solution-doc-manage-unmanaged-system-sep-1106005
https://www-secure.symantec.com/connect/downloads/sylink-replacer
https://www-secure.symantec.com/connect/downloads/script-convert-unmanaged-system-managed-system
https://www-secure.symantec.com/connect/downloads/image-installation-system-problem
2. Client communication issue.
Port is not open for the same systems Vlan. Open the port 8014 from firewall (http://management_server_address:8014/secars/secars.dll?hello,secars) Answer Come Ok then port is opened
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Troubleshooting Client Communication with SEPM
Symantec Endpoint Protection: Troubleshooting Client/Server Connectivity
3. System is power Off/Sleep Mode Manually go to the place of system and wake up the system. Wake on lan utility is alos helpfull in same.
4. System in Safe Mode.
Best solution for the safe mode is to disable this option through group policy because USB is accessible in Safe Mode and it against the security.
5. Proxy Setting issue
Below step are helpfull in in Proxy Block issue
Checked the client status: offline Took the backup of the registry Delete the following registry keys: HKEY_USER\.DEFAULT\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\Connections\DefaultConnectionSettings HKEY_USER\.DEFAULT\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\Connections\SavedLegacySettings Set the proxy enable in the registry to 0 under HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings Uncheck the proxy setting option in the internet options settings. Reboot the system. Check the client status : online/reporting to the server