You backed up original conf.properties to the same folder (i.e. <Symantec Endpoint Protection Mananger (SEPM) install folder>\tomcat\etc) and modified conf.properties for some reason, e.g. enables debug logging).
Then you restored conf.properties to original file and restarted Symantec Endpoint Protection Manager service.
Now you try to log on SEPM console, you get following error and right pane of SEPM console becomes blank.
The given URL is not valid: null
The given URL is notvalid. Could not initialize class javafx.scene.web.WebEngine
Symantec Endpoint Protection Manager 14.3
This is part of Windows User account permission issue.
Following step will add full control access to conf.properties for particular user then resolve the issue.