"Connection is invalid" exception

[Adrian Sandor]

Hi, I encountered this exception in my program:

java.lang.RuntimeException: Error accessing SimplePooledConnection. Connection 
is invalid.
        at 
com.ibatis.common.jdbc.SimpleDataSource$SimplePooledConnection.getValidConnection(SimpleDataSource.java:913)
        at 
com.ibatis.common.jdbc.SimpleDataSource$SimplePooledConnection.invoke(SimpleDataSource.java:958)
        at $Proxy7.commit(Unknown Source)
        at 
com.ibatis.sqlmap.engine.transaction.jdbc.JdbcTransaction.commit(JdbcTransaction.java:66)
        at 
com.ibatis.sqlmap.engine.transaction.TransactionManager.commit(TransactionManager.java:83)
        at 
com.ibatis.sqlmap.engine.impl.SqlMapExecutorDelegate.commitTransaction(SqlMapExecutorDelegate.java:765)
        at 
com.ibatis.sqlmap.engine.impl.SqlMapSessionImpl.commitTransaction(SqlMapSessionImpl.java:172)
        at 
com.ibatis.sqlmap.engine.impl.SqlMapClientImpl.commitTransaction(SqlMapClientImpl.java:149)

The program has a thread that is doing a very long batch transaction, 
performing executeBatch(), commitTransaction() and startBatch() every 250 
statements, and at the same time a bunch of other threads are doing LOTS of 
quick queries. Every time I run it, after several seconds that exception is 
thrown from the batch thread. What could be the problem?
(Using ibatis-2.3.0.677)

Thanks
Adrian