> Sometimes I get this exception (Firebird 1.5 with the proper Jaybird version), what is the cause of this?

What is the proper Jaybird version? Something 2.0.x or still 1.5.x?

> at org.firebirdsql.gds.GDSException: invalid request handle
> at org.firebirdsql.jgds.GDS_Impl.readStatusVector(GDS_Impl.java:1816)
> at org.firebirdsql.jgds.GDS_Impl.receiveResponse(GDS_Impl.java:1769)
> at org.firebirdsql.jgds.GDS_Impl.isc_dsql_execute2(GDS_Impl.java:917)
> at org.firebirdsql.jca.FBManagedConnection.executeStatement(FBManagedConnection.java:793)
> at org.firebirdsql.jdbc.AbstractConnection.executeStatement(AbstractConnection.java:946)
> at org.firebirdsql.jdbc.AbstractPreparedStatement.internalExecute(AbstractPreparedStatement.java:499)
> at org.firebirdsql.jdbc.AbstractPreparedStatement.executeQuery(AbstractPreparedStatement.java:109)
> at com.sikgraf.dao.OrcamentoDAO.getOcamentoBean(OrcamentoDAO.java:953)

I would suspect here some race condition in terms that two different
threads use the same connection (or statement) and then one thread
closes the connection (or statement) and another one tries to fetch data
from it.

In general this case should never happen, the checks in the driver
should prevent this.

If you have a reproducible test case, please send me or post it
somewhere for download.

Roman