Not able to access Jenkins

[Prasu S]

I'm able to login to Jenkins due to the below error. Jenkins was woking fine yesterday.I replaced the current config.xml with the previous one and restarted tomcat  but still no luck.It seems like plugin issue.  Any help is greatly appreciated.

hudson.util.HudsonFailedToLoad: org.jvnet.hudson.reactor.ReactorException: java.io.IOException: Unable to read \apps\jenkins\jenkins_home\config.xml
	at hudson.WebAppMain$3.run(WebAppMain.java:237)
Caused by: org.jvnet.hudson.reactor.ReactorException: java.io.IOException: Unable to read \apps\jenkins\jenkins_home\config.xml
	at org.jvnet.hudson.reactor.Reactor.execute(Reactor.java:269)
	at jenkins.InitReactorRunner.run(InitReactorRunner.java:44)
	at jenkins.model.Jenkins.executeReactor(Jenkins.java:915)
	at jenkins.model.Jenkins.<init>(Jenkins.java:814)
	at hudson.model.Hudson.<init>(Hudson.java:83)
	at hudson.model.Hudson.<init>(Hudson.java:79)
	at hudson.WebAppMain$3.run(WebAppMain.java:225)
Caused by: java.io.IOException: Unable to read D:\Build\Jenkins\apps\jenkins\jenkins_home\config.xml
	at hudson.XmlFile.unmarshal(XmlFile.java:165)
	at jenkins.model.Jenkins$16.run(Jenkins.java:2629)
	at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:169)
	at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:282)
	at jenkins.model.Jenkins$7.runTask(Jenkins.java:904)
	at org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:210)
	at org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:117)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:744)
Caused by: com.thoughtworks.xstream.converters.ConversionException: hudson.plugins.active_directory.ActiveDirectorySecurityRealm : hudson.plugins.active_directory.ActiveDirectorySecurityRealm
---- Debugging information ----
message             : hudson.plugins.active_directory.ActiveDirectorySecurityRealm
cause-exception     : com.thoughtworks.xstream.mapper.CannotResolveClassException
cause-message       : hudson.plugins.active_directory.ActiveDirectorySecurityRealm
class               : hudson.model.Hudson
required-type       : hudson.model.Hudson
converter-type      : hudson.util.RobustReflectionConverter
path                : /hudson/securityRealm
line number         : 935
version             : not available