Question : Intercept the "You must enter a value in the "FormName.FieldName' field." error message...

I have a "submission" form for users to enter records into.  I have a feeling they'll want to be able to go between entries and look at previous entries, etc.  So I have left the Record Selector bar on the form.  But Access does it's own message for alerting the users when they haven't filled in a required field.  I don't LIKE their error message, but I can't figure out how to intercept it.  Where is it coming from?  Since the record selector (back or forward) button is triggering it, I don't know where that event is to put in my own error message to the user.

High points given because I need an answer this weekend.  And sooner rather than later! thanks!

Answer : Intercept the "You must enter a value in the "FormName.FieldName' field." error message...

As DatabaseMX suggests Form_Error event will trap errors which you can respond, but using it isn't as straight forward as it looks.

Let's say you create Table1 with 5 fields.  Field1 and Field2 are required fields  Next you create a form where Fields 1, 2 etc. are bound to TextBox1, TextBox2 etc.  

If you enter something in text boxes 3 -5, but don't enter values in TextBox1 or TextBox2 when you attempt to update the record e.g when you select another record you'll get an error.  The error message will be  "You must enter a value in Table1.Field1" or "You must enter a value in Table1.Field1" .  So far so familiar.

The problem is that the Form_Error event will pass the same error number (3314) when TextBox1 has, a value but TextBox2 doesn't or vice versa.  So how do you let the user know which text box needs to be filled in?

Well you could make it conditional e.g

Select Case DataErr
  Case 3314
    If IsNull(TextBox1) Then
      MsgBox "TextBox1 needs a value"
   Else
     MsgBox "TextBox1 needs a value"
   End If
  Case ,,,,
    - Code
  Case Else
    Other Code
End Select

So far, so good, but lets add another manditory condition like Field1<=Field2.  You can't create a validation  rule like this in an Access table so you'd have to validate this elsewhere.  As you can see the more complex your validation becomes, the less easy it is to use the Form_Error event to do everything.

When you have complex validation you can by pass access raising data error events by validating the record using a validation function like this in Form_BeforeUpdate event  

Private Function IsValidRecord() As Boolean
On Error GoTo Err_IsValidRecord
Dim strError As String
Dim strControl As String

'Validation.
    If IsNumeric(TextBox1) And IsNumeric(TextBox2) Then
        If TextBox1 > TextBox2 Then
            strError = "TextBox1 should be less than or equal to TextBox2"
            strControl = "TextBox1"
            GoTo Error_Message_Handler
        End If
    Else
        strError = "TextBox1 should be less than or equal to TextBox2"
        strControl = "TextBox1"
        GoTo Error_Message_Handler
    End If
   
    '---------
    'Other validation code
    '----------
   
Error_Message_Handler:
    If strError = "" Then
        IsValidRecord = True
    Else
        MsgBox strError
        Me.Controls(strControl).SetFocus
    End If
   
Exit_IsValidRecord:
    Exit Function
   
Err_IsValidRecord:
    MsgBox "IsValidRecord Error: " & Err.Number & ": " & Err.Description
    Resume Exit_IsValidRecord
End Function

The Form_BeforeUpdate event fires before Form_Error event, so the following will force the user to create a valid record or bail out by clicking on an undo button

Private Sub Form_BeforeUpdate(Cancel As Integer)
  If Not IsValidRecord Then Cancel = -1
End Sub