java.io.UTFDataFormatException: Invalid byte
at org.jboss.marshalling.UTFUtils.readUTFBytes(UTFUtils.java:200)
at org.jboss.marshalling.river.RiverUnmarshaller.doReadObject(RiverUnmarshaller.java:237)
at org.jboss.marshalling.river.BlockUnmarshaller.readToEndBlockData(BlockUnmarshaller.java:111)
at org.jboss.marshalling.river.RiverUnmarshaller.doInitSerializable(RiverUnmarshaller.java:1455)
at org.jboss.marshalling.river.RiverUnmarshaller.doInitSerializable(RiverUnmarshaller.java:1431)
at org.jboss.marshalling.river.RiverUnmarshaller.doReadNewObject(RiverUnmarshaller.java:1119)
at org.jboss.marshalling.river.RiverUnmarshaller.doReadObject(RiverUnmarshaller.java:221)
at org.jboss.marshalling.river.RiverUnmarshaller.doReadObject(RiverUnmarshaller.java:158)
at org.jboss.marshalling.AbstractUnmarshaller.readObject(AbstractUnmarshaller.java:81)
at org.jboss.marshalling.river.RiverUnmarshaller.readFields(RiverUnmarshaller.java:1562)
at org.jboss.marshalling.river.RiverUnmarshaller.doInitSerializable(RiverUnmarshaller.java:1471)
at org.jboss.marshalling.river.RiverUnmarshaller.doInitSerializable(RiverUnmarshaller.java:1431)
at org.jboss.marshalling.river.RiverUnmarshaller.doReadNewObject(RiverUnmarshaller.java:1119)
at org.jboss.marshalling.river.RiverUnmarshaller.doReadObject(RiverUnmarshaller.java:221)
at org.jboss.marshalling.river.RiverUnmarshaller.doReadObject(RiverUnmarshaller.java:158)
at org.jboss.marshalling.river.RiverUnmarshaller.doReadObjectArray(RiverUnmarshaller.java:1376)
at org.jboss.marshalling.river.RiverUnmarshaller.doReadArray(RiverUnmarshaller.java:1415)
at org.jboss.marshalling.river.RiverUnmarshaller.doReadObject(RiverUnmarshaller.java:275)
at org.jboss.marshalling.river.RiverUnmarshaller.doReadObject(RiverUnmarshaller.java:158)
at org.jboss.marshalling.AbstractUnmarshaller.readObject(AbstractUnmarshaller.java:81)
at org.jboss.marshalling.river.RiverUnmarshaller.readFields(RiverUnmarshaller.java:1562)
at org.jboss.marshalling.river.RiverObjectInputStream.defaultReadObject(RiverObjectInputStream.java:65)
at java.util.concurrent.ConcurrentHashMap.readObject(ConcurrentHashMap.java:1399)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.jboss.marshalling.reflect.SerializableClass.callReadObject(SerializableClass.java:224)
at org.jboss.marshalling.river.RiverUnmarshaller.doInitSerializable(RiverUnmarshaller.java:1448)
at org.jboss.marshalling.river.RiverUnmarshaller.doReadNewObject(RiverUnmarshaller.java:1119)
at org.jboss.marshalling.river.RiverUnmarshaller.doReadObject(RiverUnmarshaller.java:221)
at org.jboss.marshalling.river.RiverUnmarshaller.doReadObject(RiverUnmarshaller.java:158)
at org.jboss.marshalling.AbstractUnmarshaller.readObject(AbstractUnmarshaller.java:81)
at org.jboss.test.marshalling.SimpleMarshallerTests$36.runRead(SimpleMarshallerTests.java:951)
at org.jboss.test.marshalling.TestBase.runReadWriteTest(TestBase.java:120)
at org.jboss.test.marshalling.SimpleMarshallerTests.testConcurrentHashMap(SimpleMarshallerTests.java:943)

Attached a test (patch against jboss marshalling trunk)