Jack Park - 2004-12-27

I've build an engine that persists three classes in three separate JDBM databases. They work fine while running. I close after the mining (filling) operation, open again to dump everything to XML. Then close the program and reopen. At that time, I can't reopen the database with this error message:
java.lang.NullPointerException
        at jdbm.recman.RecordFile.get(RecordFile.java:159)
        at jdbm.recman.LogicalRowIdManager.fetch(LogicalRowIdManager.java:136)
        at jdbm.recman.RecordManager.fetchObject(RecordManager.java:235)
        at jdbm.helper.ObjectCache.fetchObject(ObjectCache.java:104)
        at jdbm.btree.BTree.getRoot(BTree.java:452)
        at jdbm.btree.BTree.browse(BTree.java:395)
        at org.nex.text.JDBMWordGram.startPairsIterator(JDBMWordGram.java:345)

The code that does open is right out of the examples.
Any ideas greatly appreciated.

TIA
Jack