Mac OS can put .DS_Store files into the content repo directory. This can also be reproduced on Linux by creating a file under the content dir and when clean-obsolete-content() runs it will log this error. It seems it runs every 10 minutes.

----------------------

22:59:11,957 INFO  [org.jboss.as] (Controller Boot Thread) JBAS015874: JBoss EAP 6.4.5.GA (AS 7.5.5.Final-redhat-3) started in 2564ms - Started 267 of 305 services (63 services are lazy, passive or on-demand)
23:09:10,116 INFO  [org.jboss.as.repository] (ServerService Thread Pool -- 65) JBAS014903: Content /tmp/jboss-eap-6.4/standalone/data/content/7b/.DS_Store is obsolete and will be removed
23:09:10,117 ERROR [org.jboss.as.controller.management-operation] (ServerService Thread Pool -- 65) JBAS014612: Operation ("clean-obsolete-content") failed - address: ([]): java.lang.StringIndexOutOfBoundsException: String index out of range: 11
	at java.lang.String.charAt(String.java:658) [rt.jar:1.8.0_60]
	at org.jboss.as.repository.HashUtil.hexStringToByteArray(HashUtil.java:62)
	at org.jboss.as.repository.ContentReference.getHash(ContentReference.java:66)
	at org.jboss.as.repository.ContentRepository$Factory$ContentRepositoryImpl.removeContent(ContentRepository.java:368)
	at org.jboss.as.repository.ContentRepository$Factory$ContentRepositoryImpl.markAsObsolete(ContentRepository.java:424)
	at org.jboss.as.repository.ContentRepository$Factory$ContentRepositoryImpl.cleanObsoleteContent(ContentRepository.java:400)
	at org.jboss.as.server.operations.CleanObsoleteContentHandler.execute(CleanObsoleteContentHandler.java:75)
	at org.jboss.as.controller.AbstractOperationContext.executeStep(AbstractOperationContext.java:702) [jboss-as-controller-7.5.5.Final-redhat-3.jar:7.5.5.Final-redhat-3]
	at org.jboss.as.controller.AbstractOperationContext.doCompleteStep(AbstractOperationContext.java:537) [jboss-as-controller-7.5.5.Final-redhat-3.jar:7.5.5.Final-redhat-3]
	at org.jboss.as.controller.AbstractOperationContext.completeStepInternal(AbstractOperationContext.java:338) [jboss-as-controller-7.5.5.Final-redhat-3.jar:7.5.5.Final-redhat-3]
	at org.jboss.as.controller.AbstractOperationContext.executeOperation(AbstractOperationContext.java:314) [jboss-as-controller-7.5.5.Final-redhat-3.jar:7.5.5.Final-redhat-3]
	at org.jboss.as.controller.OperationContextImpl.executeOperation(OperationContextImpl.java:1144) [jboss-as-controller-7.5.5.Final-redhat-3.jar:7.5.5.Final-redhat-3]
	at org.jboss.as.controller.ModelControllerImpl.internalExecute(ModelControllerImpl.java:331) [jboss-as-controller-7.5.5.Final-redhat-3.jar:7.5.5.Final-redhat-3]
	at org.jboss.as.controller.ModelControllerImpl.execute(ModelControllerImpl.java:188) [jboss-as-controller-7.5.5.Final-redhat-3.jar:7.5.5.Final-redhat-3]
	at org.jboss.as.controller.ModelControllerImpl$3.execute(ModelControllerImpl.java:563) [jboss-as-controller-7.5.5.Final-redhat-3.jar:7.5.5.Final-redhat-3]
	at org.jboss.as.controller.ModelControllerImpl$3.execute(ModelControllerImpl.java:553) [jboss-as-controller-7.5.5.Final-redhat-3.jar:7.5.5.Final-redhat-3]
	at org.jboss.as.server.deployment.ContentRepositoryCleaner.cleanObsoleteContent(ContentRepositoryCleaner.java:132)
	at org.jboss.as.server.deployment.ContentRepositoryCleaner$ContentRepositoryCleanerTask.run(ContentRepositoryCleaner.java:67)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [rt.jar:1.8.0_60]
	at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308) [rt.jar:1.8.0_60]
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180) [rt.jar:1.8.0_60]
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294) [rt.jar:1.8.0_60]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [rt.jar:1.8.0_60]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [rt.jar:1.8.0_60]
	at java.lang.Thread.run(Thread.java:745) [rt.jar:1.8.0_60]
	at org.jboss.threads.JBossThread.run(JBossThread.java:122) [jboss-threads-2.1.2.Final-redhat-1.jar:2.1.2.Final-redhat-1]

23:09:10,120 ERROR [org.jboss.as.server] (ServerService Thread Pool -- 65) JBAS015976: Error cleaning obsolete content JBAS014749: Operation handler failed: java.lang.StringIndexOutOfBoundsException: String index out of range: 11