Terri - I was getting the same error 2-yrs ago with a paychange action and it was discussed on LawsonTalk at the following link which you may find helpful:
http://lawsontalk.com/index.php?showtopic=344&hl=I think what finally solved my problem was mapping the field numbers in addtion to the actual data that was changing. ex: Grade FLD-NBR-01 135, Rate FLD-NBR-02 62, where 135 & 62 are the Lawson field number for pay grade and pay rate.
You also may want to try loading your action manually on PA52 and doing one with your addin, then query PERSACTION table and compare the fields for the two records to see if anything is missing. Make sure you look at all fields.