[2005] System.ArgumentNullException occurred in System.dll

**This is homework, but I am not seeking help on the assignment itself**
I am get the following error in the immediate window when I run the project.

"A first chance exception of type System.ArgumentNullException occurred in System.dll" (there is no line number)

VB Code:

Imports System.Text.RegularExpressions
Public Class ReservationsForm
    Inherits System.Windows.Forms.Form
    Private Shared anInstance As ReservationsForm
    Dim checkinDate As Date
    Dim checkoutdate As Date
    Dim phoneString As String
    Dim stateString As String
    Dim zipString As String
    Dim cardString As String
    Private Sub lnameTextBox_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles lnameTextBox.Validating
        'Validate the Last Name textbox.
        With Me
            'Clear the errorprovider.
            ErrorProvider1.Clear()
            'Ensure Last Name is not blank, and is not Numeric.
            If Not Regex.IsMatch(lnameTextBox.Text, "^[a-zA-Z'`-´\s]{1,40}$") Then
                ErrorProvider1.SetError(lnameTextBox, "Please enter a Last Name. Last Name can not contain numbers.")
                lnameTextBox.SelectAll()
                lnameTextBox.Focus()
            Else
                'Ensure the error is Nothing and Clear the error provider.
                With ErrorProvider1
                    .SetError(lnameTextBox, Nothing)
                    .Clear()
                End With
            End If
        End With
    End Sub
    Private Sub fnameTextBox_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles fnameTextBox.Validating
        'Validate the First Name textbox.
        With Me
            'Clear the errorprovider.
            ErrorProvider1.Clear()
            'Ensure First Name is not blank, and is not Numeric.
            If Not Regex.IsMatch(fnameTextBox.Text, "^[a-zA-Z'`-´\s]{1,40}$") Then
                ErrorProvider1.SetError(fnameTextBox, "Please enter a first Name. First Name can not contain numbers.")
                fnameTextBox.SelectAll()
                fnameTextBox.Focus()
            Else
                'Ensure the error is Nothing and Clear the error provider.
                With ErrorProvider1
                    .SetError(fnameTextBox, Nothing)
                    .Clear()
                End With
            End If
        End With
    End Sub
    Private Sub addressTextBox_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles addressTextBox.Validating
        'Validate the address textbox.
        With Me
            'Clear the errorprovider.
            ErrorProvider1.Clear()
            'Ensure address is not blank.
            If addressTextBox.Text = "" Then
                ErrorProvider1.SetError(addressTextBox, "Please enter an address.")
                addressTextBox.SelectAll()
                addressTextBox.Focus()
            Else
                'Ensure the error is Nothing and Clear the error provider.
                With ErrorProvider1
                    .SetError(addressTextBox, Nothing)
                    .Clear()
                End With
            End If
        End With
    End Sub
    Private Sub cityTextBox_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles cityTextBox.Validating
        'Validate the City textbox.
        With Me
            'Clear the errorprovider.
            ErrorProvider1.Clear()
            'Ensure City is not blank, and is not Numeric.
            If Not Regex.IsMatch(cityTextBox.Text, "^[a-zA-Z'`-´\s]{1,40}$") Then
                ErrorProvider1.SetError(cityTextBox, "Please enter a City. City can not contain numbers.")
                cityTextBox.SelectAll()
                cityTextBox.Focus()
            Else
                'Ensure the error is Nothing and Clear the error provider.
                With ErrorProvider1
                    .SetError(cityTextBox, Nothing)
                    .Clear()
                End With
            End If
        End With
    End Sub
    Private Sub stateTextBox_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles stateTextBox.Validating
        'Validate the State textbox.
        'Ensure the State is upper case.
        stateString = stateTextBox.Text.ToUpper
        stateTextBox.Text = stateString
        With Me
            'Clear the errorprovider.
            ErrorProvider1.Clear()
            'Ensure State is not blank, and is not Numeric.
            If Len(stateString) <> 2 OrElse Not Regex.IsMatch(stateString, "^[A-Z]{1,40}$") Then
                ErrorProvider1.SetError(stateTextBox, "Please enter a State. State can not contain numbers.")
                stateTextBox.SelectAll()
                stateTextBox.Focus()
            Else
                'Ensure the error is Nothing and Clear the error provider.
                With ErrorProvider1
                    .SetError(stateTextBox, Nothing)
                    .Clear()
                End With
            End If
        End With
    End Sub
    Private Sub phoneTextBox_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles phoneTextBox.Validating
        'Validate the Phone textbox.
        'Mask set to numeric, no need to check for alpha characters.
        phoneString = phoneTextBox.Text
        With Me
            'Clear the errorprovider.
            ErrorProvider1.Clear()
            'Ensure Phone number is not blank, and contains all 10 digits.
            If Len(phoneString) < 13 Then
                ErrorProvider1.SetError(phoneTextBox, "Phone number must contain 10 digits.")
                phoneTextBox.SelectAll()
                phoneTextBox.Focus()
            Else
                'Ensure the error is Nothing and Clear the error provider.
                With ErrorProvider1
                    .SetError(phoneTextBox, Nothing)
                    .Clear()
               End With
            End If
        End With
    End Sub
   Private Sub zipTextBox_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles zipTextBox.Validating
        'Validate the zip code.
        'Mask set to numeric, no need to check for alpha characters.
        zipString = zipTextBox.Text
        With Me
            'Clear the errorprovider.
            ErrorProvider1.Clear()
            'Ensure Zip Code is numeric and contains all 5 digits.
            If Not IsNumeric(zipTextBox.Text) OrElse Not Len(zipString) = 5 Then
                ErrorProvider1.SetError(zipTextBox, "Zip Code must contain 5 digits.")
                zipTextBox.SelectAll()
                zipTextBox.Focus()
            Else
                'Ensure the error is Nothing and Clear the error provider.
                With ErrorProvider1
                    .SetError(zipTextBox, Nothing)
                    .Clear()
               End With
            End If
        End With
    End Sub
    Private Sub checkInDateTimePicker_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles checkInDateTimePicker.Validating
        'Validate the check in date.
        With Me
            'Clear the errorprovider.
            ErrorProvider1.Clear()
            checkinDate = .checkInDateTimePicker.Value
            If checkinDate < Date.Now.Date Then
                ErrorProvider1.SetError(checkInDateTimePicker, "Check in date can not be less than todays date.")
                .checkInDateTimePicker.Focus()
            Else
                'Ensure the error is Nothing and Clear the error provider.
                With ErrorProvider1
                    .SetError(checkInDateTimePicker, Nothing)
                    .Clear()
                End With
            End If
        End With
    End Sub
    Private Sub checkOutDateTimePicker_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles checkOutDateTimePicker.Validating
        'Validate the check out date.
        With Me
            'Clear the errorprovider.
            ErrorProvider1.Clear()
            checkoutdate = .checkOutDateTimePicker.Value
            If Not checkoutdate > checkinDate Then
                ErrorProvider1.SetError(checkOutDateTimePicker, "Check out date must be greater than check in date.")
                .checkOutDateTimePicker.Focus()
            Else
                'Ensure the error is Nothing and Clear the error provider.
                With ErrorProvider1
                    .SetError(checkOutDateTimePicker, Nothing)
                    .Clear()
                End With
            End If
        End With
    End Sub
    Private Sub cardTypeComboBox_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles cardTypeComboBox.Validating
        'Validate Card Type.
        With Me
            'Clear the errorprovider.
            ErrorProvider1.Clear()
            If .cardTypeComboBox.SelectedIndex = -1 Then
                ErrorProvider1.SetError(cardTypeComboBox, "Please select a Card Type.")
                .cardTypeComboBox.Focus()
            Else
                'Ensure the error is Nothing and Clear the error provider.
                With ErrorProvider1
                    .SetError(cardTypeComboBox, Nothing)
                    .Clear()
                End With
            End If
        End With
    End Sub
      End Sub

You don't have to worry about first chance exceptions. The debugger will notify you every time an exception is thrown. That's a first chance exception, because it's the first chance to catch it. If that exception is caught and the exceptional situation handled then execution continues. If the exception is not caught in code then the debugger is offered a second chance to catch the exception, at which point it shows you the unhandled exception dialogue. In your case, that exception is being thrown and caught within the Framework itself. You're notified that it occurred but you don't have to worry about it.

Thank you jmcilhinney.