我已经在集群模式下配置了cassandra-1.2.2。但是在用我的cassandra配置启动titan时，它显示了以下异常

Exception in thread "main" java.lang.IllegalArgumentException: Could not instantiate implementation: com.thinkaurelius.titan.diskstorage.cassandra.astyanax.AstyanaxStoreManager
    at com.thinkaurelius.titan.diskstorage.Backend.getImplementationClass(Backend.java:268)
    at com.thinkaurelius.titan.diskstorage.Backend.getStorageManager(Backend.java:226)
    at com.thinkaurelius.titan.diskstorage.Backend.<init>(Backend.java:97)
    at com.thinkaurelius.titan.graphdb.configuration.GraphDatabaseConfiguration.getBackend(GraphDatabaseConfiguration.java:406)
    at com.thinkaurelius.titan.graphdb.database.StandardTitanGraph.<init>(StandardTitanGraph.java:62)
    at com.thinkaurelius.titan.core.TitanFactory.open(TitanFactory.java:40)
    at com.thinkaurelius.titan.tinkerpop.rexster.RexsterTitanServer.start(RexsterTitanServer.java:70)
    at com.thinkaurelius.titan.tinkerpop.rexster.RexsterTitanServer.startDaemon(RexsterTitanServer.java:80)
    at com.thinkaurelius.titan.tinkerpop.rexster.RexsterTitanServer.main(RexsterTitanServer.java:118)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at com.thinkaurelius.titan.diskstorage.Backend.getImplementationClass(Backend.java:257)
    ... 8 more
Caused by: com.thinkaurelius.titan.diskstorage.TemporaryStorageException: Temporary failure in storage backend
    at com.thinkaurelius.titan.diskstorage.cassandra.astyanax.AstyanaxStoreManager.ensureKeyspaceExists(AstyanaxStoreManager.java:394)
    at com.thinkaurelius.titan.diskstorage.cassandra.astyanax.AstyanaxStoreManager.<init>(AstyanaxStoreManager.java:164)
    ... 13 more
Caused by: com.netflix.astyanax.connectionpool.exceptions.NoAvailableHostsException: NoAvailableHostsException: [host=None(0.0.0.0):0, latency=0(0), attempts=0] No hosts to borrow from
    at com.netflix.astyanax.connectionpool.impl.RoundRobinExecuteWithFailover.<init>(RoundRobinExecuteWithFailover.java:31)
    at com.netflix.astyanax.connectionpool.impl.TokenAwareConnectionPoolImpl.newExecuteWithFailover(TokenAwareConnectionPoolImpl.java:74)
    at com.netflix.astyanax.connectionpool.impl.AbstractHostPartitionConnectionPool.executeWithFailover(AbstractHostPartitionConnectionPool.java:229)
    at com.netflix.astyanax.thrift.ThriftClusterImpl.executeSchemaChangeOperation(ThriftClusterImpl.java:131)
    at com.netflix.astyanax.thrift.ThriftClusterImpl.addKeyspace(ThriftClusterImpl.java:252)
    at com.thinkaurelius.titan.diskstorage.cassandra.astyanax.AstyanaxStoreManager.ensureKeyspaceExists(AstyanaxStoreManager.java:389)
    ... 14 more

请帮忙找出你的毛病？