There's a language problem here, of course, that makes following things somewhat difficult, but I'm guessing that 'nieuwe vergadering' means 'enter new record;' is that right?
At any rate, I can't find any button named 'nieuwe vergadering' on this form, nor is there the Access native 'Add Record' button on frmOBNCieOvz.
There is a native Add Record on the Subform, sfrmOBNCieOvz, and the reason that you cannot add Records (or edit, for that matter) is that on this Subform is that the Controls named DTLidNaam, Formulier and Deelname each have their Locked Properties set to Yes.
Just out of curiosity, what language are we dealing with here?
Linq ;0>