Date validation rule. Not more than 1 month bigger than value in

You can try this in the forms BEFORE update

Private Sub Form_BeforeUpdate(Cancel As Integer)
If Me.LastBookedDate > DateAdd("m", 1, DFirst("LastBookedDate", "tblSystem")) Then
    MsgBox "Date wrong"
    Cancel = True
End If

End Sub

q-lastbookeddate is not linked or a part of the private sub form, is that the problem I have in this line (It does not understand Me.LastBookedDate)
If Me.LastBookedDate > DateAdd("m", 1, DFirst("LastBookedDate", "tblSystem")) Then...

Secondly I have the feeling that vba does not "like" -(score, I think it is called), which might be a problem due to the fact that my query and table names all uses eg. t-reg, q-lastbookeddate..?
TIA

Me.LastBookedDate is the name of the field on your form

LastBookedDate in the dlookup function is the name of the field in your table which in this example is tblSystem

You should try and give your tables/fields etc names WITHOUT - and try and keep to english characters a-z 0-9

If you still cant get it working then you are welcome to send your dB to me

eksperten@NOSPAMsanthell.dk
remove NOSPAM

Thanks a LOT! :-) It is so beautiful... Have a nice Christmas and a Happy new year. (I might be back before that, but anyway)

you have a good Xmas an dnew year too

and thanks