Carsten,

> At the second costumer site i've installed Firebird 1.5.2RC1 and
> Jaybird 1.5.4. But now the error happens every day.
> It's not reproducable, because everytime it happens in another
> db-operation, but after that the connection is not usable anymore
> and the connection pool returns this invalid connection everytime.

> org.firebirdsql.jdbc.FBSQLException: GDS Exception. 335544344. I/O error
> for file ReadFile "E:\IB_DATENBANK\DBAMS_THT_L.GDB" Error while trying to
> read from file null

This is an error from the server (check the server logs). We cannot do
anything here.

> org.firebirdsql.jdbc.FBSQLException: GDS Exception. 335544327. invalid
> request handle

Try setting pingInterval=10 (or any other small value). This will cause pool
to ping connection each time it is returned from the pool. After the I/O
error first ping should eliminate connection from the pool. If this does not
happen, please report a bug.

Roman