When does a PreparedStatement become invalid in derby?

[V Narayanan]

Hi,
I am working on StatementEventListeners as part of providing JDBC4.0
support to derby.

       The driver calls the statementErrorOccurred method on all
StatementEventListeners registered on the connection when it detects
that a PreparedStatement is invalid.

       One situation when this happens is when the connection is closed.
 what other circumstances can make the PreparedStatement invalid?

thanx
V.Narayanan