Solr Exception

Been trying to get this working for me today with no luck.
When I try to 'Index now' on my node index, I get told: 'Couldn't index items. Check the logs for details.'

The log contains the following error:
"An error occurred while indexing: "500" Status: Internal Server Error: Internal Server Error

HTTP Status 500 - /var/solr/example/solr/data/index/_0.fdt (Permission denied) java.io.FileNotFoundException: /var/solr/example/solr/data/index/_0.fdt (Permission denied) at java.io.RandomAccessFile.open(Native Method) at java.io.RandomAccessFile.(RandomAccessFile.java:233) at org.apache.lucene.store.SimpleFSDirectory$SimpleFSIndexOutput.(SimpleFSDirectory.java:186) at org.apache.lucene.store.NIOFSDirectory.createOutput(NIOFSDirectory.java:76) at org.apache.lucene.index.FieldsWriter.(FieldsWriter.java:61) at org.apache.lucene.index.StoredFieldsWriter.initFieldsWriter(StoredFieldsWriter.java:66) at org.apache.lucene.index.StoredFieldsWriter.finishDocument(StoredFieldsWriter.java:144) at org.apache.lucene.index.StoredFieldsWriter$PerDoc.finish(StoredFieldsWriter.java:189) at org.apache.lucene.index.DocumentsWriter$WaitQueue.writeDocument(DocumentsWriter.java:1574) at org.apache.lucene.index.DocumentsWriter$WaitQueue.add(DocumentsWriter.java:1593) at org.apache.lucene.index.DocumentsWriter.finishDocument(DocumentsWriter.java:1165) at org.apache.lucene.index.DocumentsWriter.updateDocument(DocumentsWriter.java:834) at org.apache.lucene.index.DocumentsWriter.updateDocument(DocumentsWriter.java:809) at org.apache.lucene.index.IndexWriter.updateDocument(IndexWriter.java:2683) at org.apache.lucene.index.IndexWriter.updateDocument(IndexWriter.java:2655) at org.apache.solr.update.DirectUpdateHandler2.addDoc(DirectUpdateHandler2.java:241) at org.apache.solr.update.processor.RunUpdateProcessor.processAdd(RunUpdateProcessorFactory.java:61) at org.apache.solr.handler.XMLLoader.processUpdate(XMLLoader.java:139) at org.apache.solr.handler.XMLLoader.load(XMLLoader.java:69) at org.apache.solr.handler.ContentStreamHandlerBase.handleRequestBody(ContentStreamHandlerBase.java:54) at org.apache.solr.handler.RequestHandlerBase.handleRequest(RequestHandlerBase.java:131) at org.apache.solr.core.SolrCore.execute(SolrCore.java:1316) at org.apache.solr.servlet.SolrDispatchFilter.execute(SolrDispatchFilter.java:338) at org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:241) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:558) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) at java.lang.Thread.run(Thread.java:636)"

I'm not really sure how to diagnose the problem. As far as I can tell I followed all setup instructions accurately.