jdbc/callable statment error

When executing the following statments from netbeans 4.1 sun app server 8.1

CallableStatement proc = con.prepareCall("{ ? = call test_function ( ? ) }");
proc.registerOutParameter(1, Types.BOOLEAN);
proc.setString(2, "testthis");
proc.execute();

This shows up in my server log.

LOG: statement: select * from test_function ( 'thisTest' ) as result;
ERROR: function test_function("unknown") does not exist
HINT: No function matches the given name and argument types. You may need to add explicit type casts.

And I get an exception from my app server that states "No function" etc, etc...

Now, if I cut and paste that into my psql terminal it appears to work... So I'm really curious as to why it doesn't work through jdbc...

Couple of things: I'm getting my connection through a connection pool on my app server and that appears to be in working order...

Any suggestions?

Gary Lucas