Log in to an ADFS Single Sign On (SSO) environment.
An error 500 is returned with a java.lang.NullPointerException with a full stack trace reported in the logs.

A new user was added to the configuration file:
WEB-INF\LiveContentGroups.xml 

user in Browser sees:

Tomcat log file localhost.2018-02-08.log shows the simplified error as"

08-Feb-2018 15:12:26.467 SEVERE [localhost-startStop-1] org.apache.catalina.core.StandardContext.filterStart Exception starting filter LCFilter
 javax.servlet.ServletException: MappingsFile could not be parsed
	at com.sdl.cd.livecontent.sso.LCFilter.init(LCFilter.java:118)
	at org.apache.catalina.core.ApplicationFilterConfig.initFilter(ApplicationFilterConfig.java:279)
	at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:260)
	at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:105)
	at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4689)
	at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5329)
	at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
	at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:725)
	at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:701)
	at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:717)
	at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1092)
	at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1834)
	at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
	at java.util.concurrent.FutureTask.run(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)
Caused by: com.sdl.cd.livecontent.sso.SSOException: [SSO] Fatal Error: Failed to parse C:\Program Files\Apache Software Foundation\Tomcat 8.0\webapps\LiveContent\WEB-INF/LiveContentGroups.xml
	at com.sdl.cd.livecontent.sso.LCGroupMapper.parseMappingsFile(LCGroupMapper.java:82)
	at com.sdl.cd.livecontent.sso.LCFilter.init(LCFilter.java:116)
	... 16 more

Opened notepad ++ and used plug 'XMLTools' to parse the LiveContentGroups.xml file
found a comment line

<-- comment --->

Line contained three dashes what caused the parsing error for the XML file.

extra character in XML file left it unable to parse