Odd field data type error

I have an agent used to clear the pwd digest field on person docs (code below). I call this agent from another agent and use the RunOnServer method so I can run the agent with an admin ID that has full access. On most person docs it works fine but on some it raises an error :4000 - Notes error: field in note has wrong datatype". The error occurs when it hits the ComputeWithForm line. If I comment out the line it works without error but the data type of “Text” changes to “Text List” when it gets saved. If I open the person doc and save it manually the data type goes back to “Text”. If I run the agent on other person docs it saves as “Text”. What would cause some person docs to raise the error? I don’t see any difference between them and they all use the same form.

Dim ns As New NotesSession

Dim agent As NotesAgent

Set agent = ns.CurrentAgent

Dim db As NotesDatabase

Dim doc As NotesDocument

Set db = ns.CurrentDatabase

Set doc = db.GetDocumentByID(agent.ParameterDocID)

nam$ = doc.LastName(0) & ", " & doc.FirstName(0)

doc.PasswordDigest = ""

Call doc.ComputeWithForm(1,1) 'error occurs here

Call doc.Save(1,1)

Print "pwd digest cleared for " & nam$

Exit Sub