Does the database table skedulering2 have a field called Slaag?


By the way, the variables kode and beskrywing don't seem to have a purpose, they just make the code harder to read. I recommend removing them, and altering the .CommandText to include the values directly, ie:
Code:
            opdragskepkode.CommandText = "UPDATE skedulering2 " &
                                    "SET GroeperingsKode        = CONCAT( '', GrSl) , " &
                                    "GroepperingsBeskrywing     = CONCAT( '', Slaag) ;"