ClassCastException on every login coming from server

We're use the server and JSON.
It's been running quite happily for quite awhile (I think we went to JSON in December).
Today we are all receiving an error message at login.
I restarted the server and two of these happened.
(I attempted to login twice!)

Did something get corrupted in the DB?
Some userdata maybe?

Any help would be appreciated.
Of course, it's Friday and I won't get back to this 'till Monday.

-Dan

java.lang.ClassCastException: agiletrack.data.record.History

at agiletrack.server.persistence.TrackerPersistenceDefault.generateUserSummary(TrackerPersistenceDefault.java:191) at agiletrack.server.persistence.TrackerPersistenceDefault.generateRecordSummary(TrackerPersistenceDefault.java:99) at agiletrack.server.persistence.TrackerCachedPersistence.generateRecordSummary(TrackerCachedPersistence.java:126) at agiletrack.server.TrackerModel.getRecordSummary(TrackerModel.java:924) at agiletrack.server.TrackerModel.processRecordSummary(TrackerModel.java:818) at agiletrack.server.TrackerModel.getRecord(TrackerModel.java:800) at agiletrack.server.http.TrackerJSONRPCController.load(TrackerJSONRPCController.java:109) at sun.reflect.GeneratedMethodAccessor2.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:585) at agiletrack.server.http.JSONRPCServer.execute(JSONRPCServer.java:75) at agiletrack.server.http.TrackerJSONRPCStreamServer$1.run(TrackerJSONRPCStreamServer.java:85) at java.lang.Thread.run(Thread.java:595)

—Posted by Dan (I'm such an ogre) Mullen on Apr 18, 2008