Before Update Code Being Ignored (1 Viewer)

'------------------------------------------------------------
' Form_BeforeUpdate(Cancel As Integer)
' Validation that requires user to enter first name, last
' name and username to save a record.
'
'------------------------------------------------------------

Private Sub Form_BeforeUpdate(Cancel As Integer)

If Len([txtFirstName] & vbNullString) = 0 Then
    [COLOR=red]MsgBox "Please enter a First Name.", vbOK + vbExclamation + 
[/COLOR]  vbDefaultButton2, "Empty Field"

ElseIf Len([txtLastName] & vbNullString) = 0 Then
    [COLOR=red]MsgBox "Please enter a Last Name.", vbOK + vbExclamation + 
[/COLOR]  vbDefaultButton2, "Empty Field"

ElseIf Len([txtUserID] & vbNullString) = 0 Then
   [COLOR=red]MsgBox "Please enter a UserID Name.", vbOK + vbExclamation +[/COLOR] 
    vbDefaultButton2, "Empty Field"
End If

If Not IsNull(Me.txtFirstName) Then
    If Not IsNull(Me.txtLastName) Then
        If Not IsNull(Me.txtUserID) Then
            MsgBox "A new user has been successfully added to the 
             [COLOR=red]database.", vbInformation + vbOKOnly, "User Update"
[/COLOR]      End If
    End If
End If
End Sub

Option Compare Database
Option Explicit

Option Compare Database
Option Explicit