Did anyone make any changes to the linked table such as add a field with a data type that Access doesn't like? Or add a PK with Identity set to "no". Can you edit a record? I'd try creating a new db with only that table in it and try to add or edit after determining if you can edit the current connection. Don't know if you're using ODBC to connect or what, but if you can edit other tables, I guess it's not an issue of rights having being altered.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.