When I am adding a new record to a table (using a form based on a query) I first use the command:
DoCmd.GoToRecord , , acNewRec
Then, when I try to type a value into a field (not a key field) I get the message: "Field cannot be updated".
The underlying table field is a "required" field with validation rule (in the table definition) of "Is Not Null".
If I respond to the message by clicking "OK" the field on the form then accepts the character that triggered the message and lets me enter the field value.