Hi,
what happens in "com.et.GestionDeStockClient.main(GestionDeStockClient.java:30)"? Unfortunately, the error message does not tell anything about the missing class, so it is hard to say whether this is related to your EJBs.
Could you check that both EJB jar and client JAR contain all class files of your entities, and both use the same versions (same compilation date)?
Best regards
Wolfgang