"When a record is created or updated, but not in both cases"

I imagine that everyone has seen a permissions error before:
[INDENT]You do not have permissions to set a value for element custentitypi_url 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.[/INDENT]

Could someone tell me how I can tell if condition "3" is true? I'm fairly certain 1 and 2 are false.

I'm trying to set a custom field on a contact, and I don't see anything in the Netsuite customization interface that specifies if a field should be settable on create vs update. I'm using the SOAP API, and have successfully set a custom field in one Netsuite account, but am seeing this error in a second account (that had some customization done by a third party during implementation). My best guess is that the forms or entities are misconfigured somehow.