I had my server set up for user/password authentication, and UAExpert was connected.
I think changed the server to allow no authentication, restarted it, and tried to reconnect with UAExpert. It asked me for a password during the connection process, and then failed to reconnect. This is the exception I’m seeing on the server side:

2013-05-02 08:35:27,591[Blocking-Work-Executor-4] ERROR – While handling ActivateSessionRequest (id=1905594162)
UserTokenSignature=SignatureData (id=1897453023)
Signature=null
Algorithm=null
LocaleIds=class java.lang.String[1]
[0]=en
ClientSoftwareCertificates=class org.opcfoundation.ua.core.SignedSoftwareCertificate[0]
ClientSignature=SignatureData (id=360799611)
Signature=null
Algorithm=null
UserIdentityToken=ExtensionObject (id=1612726596)
encodeType=EncodeType (id=1704790185)
ordinal=0
name=Binary
object=byte[] (id=493558071)
typeId=NodeId (id=1648654583)
value=UnsignedInteger (id=2103562887)
value=324
type=IdType (id=558161248)
ordinal=0
name=Numeric
namespaceIndex=0
hash=1142157539
RequestHeader=RequestHeader (id=807525040)
AuditEntryId=null
AuthenticationToken=NodeId (id=2124181887)
value=UnsignedInteger (id=1356827081)
value=1
type=IdType (id=558161248)
namespaceIndex=0
RequestHandle=UnsignedInteger (id=63902874)
value=8
Timestamp=DateTime (id=273779818)
value=130119717275886928
AdditionalHeader=null
ReturnDiagnostics=UnsignedInteger (id=775468697)
value=0
TimeoutHint=UnsignedInteger (id=1507429252)
value=10000

ServiceFault: Bad_InternalError (0x80020000) “An internal error occurred as a result of a programming or configuration error.”
Diagnostic Info: java.lang.NullPointerException
at com.prosysopc.ua.UserIdentity.decryptPassword(Unknown Source)
at com.prosysopc.ua.server.SessionManager$ServerUserIdentity.(Unknown Source)
at com.prosysopc.ua.server.SessionManager.activateSession(Unknown Source)
at com.prosysopc.ua.server.SessionServiceHandler.onActivateSession(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at org.opcfoundation.ua.application.ServiceHandlerComposition$1.serve(Unknown Source)
at org.opcfoundation.ua.application.ServiceHandlerComposition.serve(Unknown Source)
at org.opcfoundation.ua.transport.tcp.nio.UATcpServer$UATcpServerConnection$UATcpServerSecureChannel.onSecureMessage(Unknown Source)
at org.opcfoundation.ua.transport.tcp.nio.UATcpServer$UATcpServerConnection.onSecureMessage(Unknown Source)
at org.opcfoundation.ua.transport.tcp.nio.UATcpConnection$3.onMessageComplete(Unknown Source)
at org.opcfoundation.ua.transport.tcp.nio.SecureInputMessageBuilder.fireComplete(Unknown Source)
at org.opcfoundation.ua.transport.tcp.nio.SecureInputMessageBuilder.setMessage(Unknown Source)
at org.opcfoundation.ua.transport.tcp.nio.SecureInputMessageBuilder$1.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:722)

at org.opcfoundation.ua.application.ServiceHandlerComposition$1.serve(Unknown Source)
at org.opcfoundation.ua.application.ServiceHandlerComposition.serve(Unknown Source)
at org.opcfoundation.ua.transport.tcp.nio.UATcpServer$UATcpServerConnection$UATcpServerSecureChannel.onSecureMessage(Unknown Source)
at org.opcfoundation.ua.transport.tcp.nio.UATcpServer$UATcpServerConnection.onSecureMessage(Unknown Source)
at org.opcfoundation.ua.transport.tcp.nio.UATcpConnection$3.onMessageComplete(Unknown Source)
at org.opcfoundation.ua.transport.tcp.nio.SecureInputMessageBuilder.fireComplete(Unknown Source)
at org.opcfoundation.ua.transport.tcp.nio.SecureInputMessageBuilder.setMessage(Unknown Source)
at org.opcfoundation.ua.transport.tcp.nio.SecureInputMessageBuilder$1.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:722)
Caused by: java.lang.NullPointerException
at com.prosysopc.ua.UserIdentity.decryptPassword(Unknown Source)
at com.prosysopc.ua.server.SessionManager$ServerUserIdentity.(Unknown Source)
at com.prosysopc.ua.server.SessionManager.activateSession(Unknown Source)
at com.prosysopc.ua.server.SessionServiceHandler.onActivateSession(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
… 11 more

If I change the server settings on UAExpert to anonymous connection, things work again. Is this a bug, or do I need to handle something differently?
When the problem happens, my onValidate is never called.