1. Check the Form's RecordSource. If it is a Query / SQL String, it may
not be updateable. Open the Query / SQL String by itselft, i.e. not through
the Form and see if you can update the data in the DatasheetView of the
Query. The Query may not be updateable and therefore the data on the Form
is not updateable.
If this is the case, check Access Help on "Updatable Query".
2. If the Query is updateable, check the Form's AllowAdditions and
AllowEdits Property.