This record is called "configuratienummer" (without quotes).
do you mean record or table?
if you mean table i think i can under stand what your trying to do
how i see it is that you get an error when you append a already excisting name to the table,
now i see too possible solutions 1 easy 1 hard
suppress the error
the method you've suggested
firstly enter the VBA editior goto tool --> references and ensure that microsoft DAO 3.6 is ticked
then add this code to the txtboxes after update event
Dim Cur_DB As DAO.Database, Record_Set As DAO.Recordset
Set Cur_DB = CurrentDb
Set Record_Set = Cur_DB.OpenRecordset("select * from configuratienummer where <fieldname> = ;")
If Record_Set.RecordCount <> 0 Then MsgBox "Already exists"
you may need to covert some of this into the native langueage you using (i'd say german from the table name)
Definition of a Beginner, Someone who doesn't know the rules.
Definition of an Expert, Someone who knows when to ignore the rules.