Problem calling a stored procedure from a Java program

I have an external stored procedure written in SQL/RPG LE returning a result set. When I debug the program everything seems to work well. However, when I call the stored procedure from a Java program, while looping through the result set, exceptions are thrown. It looks like some of the fields are retuned as null values. While using a tool such as DbVisualizer and executing the stored procedure the result set displayed is a mixture of null and garbage values for most of the columns. I have created the stored procedure using the following statement:

 
               CREATE PROCEDURE P1 
              (IN PARM1 CHAR(7), 
               PARM2 CHAR(12)) 
               RESULT SETS 1 
               EXTERNAL NAME dcheri/SHIPBUILD 
                 PARAMETER STYLE SQL 
               LANGUAGE RPGLE; 

The external program was compiled as a module and then a program object was created using CRTPGM PGM(DCHERI/SHIPBUILD) ACTGRP(*CALLER). Please let me know what I am doing wrong.