Attempting to use CALCULATE or MOVEITEM to update relate items in an Access table produces this error:
No update operation allowed without Unique Id.
Cannot perform update. Related file is opened Read Only. (RDBENC)
The Access table needs to have a primary key specified.
Open the table in Access and specify the relate column as a primary key.
Open the table you wish to work with in design view and select the field you wish to designate as the primary key field. The unique index is created automatically.