PSQLException Can't infer the SQL type to use with Native Query call

In trying to call a postgresql 8.4 stored function I am passing a
class as well as a List (I have to save a master record as well as the
detail records). This is being done with a native query using
EclipseLink 2.1. However, I am getting back a message for the first
item:

PSQLException: Can't infer the SQL type to use for an instance of
com.hwcs.veri.shared.dto.MyClass. Use setObject() with an explicit
Types value to specify the type to use.

I am calling the query setting up the parameter with:

query.setParameter( 1, myClass );

The receiving stored function has the following:

 FUNCTION perform_schema.saveInfo( newrec    boolean,
                                  myClass   <user defined type>,
                  myDtl     <user defined type>[] )

I am unclear how to setup the pass fromm eclipselink to postgresql.
Does anyone have any suggestions or can point to docs which speak to
this specifically?

Thanks