I've not done this but would expect that
a) you cannot alter a table field using a recordset field reference
b) you cannot alter a table field when there is a hold on it by way of query, recordset, form, report, whatever
and you are doing both of these things.
If the table field does not have the property you're trying to alter, then you must create it first. Just saying that in for future reference in case you're not aware. I don't know if a table field has this property if it has never been set. On the other hand, if this is a one-off, why don't you just change it in design view?
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.