How are you accessing the table? Dirctly through access or through an ASP.net page (or similar).
If its through an ASP.net page make sure that the connection is opened and then closed correctly in each opreation. If it remains open it can cause the table to lock and will not allow any further modifcaiton to it until it is closed.
Also have a look at the relationships in your database. If the edit you are trying to do creates a duplicate, or requires data in another table, it will not be allowed until the correct data is entered.
DJ