More information.

When you use .open property without specifying any cursor and lock types, the default will be adOpenForwardOnly and adLockReadOnly, repectively. Therefore, if you want to update, you have to specify one of these arguments.

Cursor Type: adOpenKeyset, adOpenDynamic, and adOpenStatic

Lock Type: adLockPessimistic, adLockOptimistic, and adLockBatchOptimistic