Which Error?
Anyway I don't think you can't achieve your duty like that. In my mind such property can only be set when you create a Table.
Once a table exists and contains data, you must use an SQL statement "ALTER TABLE" in a query.
Unfortunately, I don't find the syntax to set the DecimalPlaces property of a field through ALTER TABLE.
When you change using only VBA code, you must:
Create a NEW field with the new property (ies)
Copy the data of each record from the old to the new field
Delete the old field
Rename the new field as the old one
This would work easily if you no relationship nor indexes on this field....