Seems to be a problem with the underlying Space code when in a cluster. Seems very similar to CONF-9371. The customer was using the RSS feed macro at the time. Removed the macro and had to restart each node.

2007-10-30 02:06:39,842 ERROR [TP-Processor25] [atlassian.confluence.security.PermissionCheckDispatcher] isPermitted Unable to determine permissions for /pages/doexportpage.action?pageId=657284&type=TYPE_PDF: java.util.ConcurrentModificationException
– url: /confluence/display/TEST/noishii | userName: anonymous
java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:841)
at java.util.HashMap$EntryIterator.next(HashMap.java:883)
at java.util.HashMap$EntryIterator.next(HashMap.java:881)
at java.util.HashMap.writeObject(HashMap.java:1037)
at sun.reflect.GeneratedMethodAccessor214.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:917)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1339)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1290)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1079)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:302)
at com.tangosol.util.ExternalizableHelper.writeSerializable(ExternalizableHelper.java:2100)
at com.tangosol.util.ExternalizableHelper.internalWriteObject(ExternalizableHelper.java:2481)
at com.tangosol.util.ExternalizableHelper.toBinary(ExternalizableHelper.java:166)
at com.tangosol.coherence.component.util.daemon.queueProcessor.service.ReplicatedCache.requestUpdate(ReplicatedCache.CDB:21)
at com.tangosol.coherence.component.util.daemon.queueProcessor.service.ReplicatedCache.updateResource(ReplicatedCache.CDB:68)
at com.tangosol.coherence.component.util.CacheHandler.put(CacheHandler.CDB:11)
at com.tangosol.coherence.component.util.CacheHandler.put(CacheHandler.CDB:1)
at com.tangosol.coherence.component.util.SafeNamedCache.put(SafeNamedCache.CDB:1)
at com.atlassian.confluence.cache.tangosol.TangosolCache.put(TangosolCache.java:42)
at com.atlassian.confluence.security.PermissionCheckDispatcherResultCache.putInCache(PermissionCheckDispatcherResultCache.java:60)
at com.atlassian.confluence.security.PermissionCheckDispatcher.isPermitted(PermissionCheckDispatcher.java:52)
at sun.reflect.GeneratedMethodAccessor541.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:260)
at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:207)