Need to Circumvent general Microsoft Access Error?

[Heatshiver]

I have a field to input a User ID. It is validated by another table where all the User ID's are stored. The code I have inserted works and makes sure that the user receives a message to describe the problem:

Private Sub UserID_AfterUpdate()

If IsNull(DLookup("UserNum", "tblUsers", "UserNum = '" & [Forms]![frmGenSum]![UserID] & "'")) Then
MsgBox "Please input a valid User ID."
[Forms]![frmGenSum]![UserID] = ""
Else
'Do Nothing
End If



End Sub

The problem I am having is that Microsoft has its own error message after mine: "You cannot add or change a record because a related record is required in table 'tblUsers'." I need to a way to avoid the Microsoft statement altogether. I was trying On Error GoTo and then the If statement, but it still comes up.

What VBA coding can I use to circumvent this? Thanks for the help.

[Heatshiver]

Figured out a solution.

I technically don't need to place the code in the text box because I have a save button. If I just use the save button, the error does not appear.

However, I have no exit button on the form, and in order to get away from that form the user must use the Back button which closes the form.

I also had to set the form itself to cycle only through the record it was in, otherwise it would try to get to a new record and then give the error.