Creating Relationship

I am having a problem with creating a relationship between two item types.  I have an extension to projects where we have our own part record (HPP) with additional data.  The relationship between that HPP part record and the project is done through the UI and is set correctly.  I have a web service that retrieves data from our ERP application and in that web service, I have the ID of the HPP part record so that I can get it immediately after returning from the web service.  I have written data to a debug log and that shows that I do have the actual HPP record that I am expecting to see.  I now want to create my own related customer (HPC) record and relate it to the HPP record.  In the code that is executing, I am correctly creating the HPC record (again, dumping the data to log files).  However, the relationship record(HPPC)  is not being created.  Here is my code that is executing:   As noted before HPP and HPC are valid records with valid IDs. Item partCustLink = HPP.createRelationship("HPPC", "add"); partCustLink.setRelatedItem(HPC); partCustLink.apply(); Can anyone throw any light on why the HPPC record is not being created? TIA