nlapiCopyRecord problem

I am trying to use a form I've built to copy an entity record, change a few fields, and submit the new record, but I get an INSUFFICIENT_PERMISSION error on submit.
The details say:
You do not have permissions to set a value for element contactoroles.contactname due to one of the following reasons: 1) the field is read-only; 2) An associated feature is disabled; 3) The field is available either when a record is created or updated, but not in both cases.

This only happens on entities with contacts (as opposed to those without any)

I believe this is the result of nlapiSubmitRecord trying to enter lines on the 'access' sublist, which is supposed to be populated internally from the 'contacts' sublist. I'm not entirely sure of this, however.