[RESOLVED] Extract filename from textbox

[VB.NET Developer]

I want to extract filename from textbox´s filepath, but it does not work.
InputFile is read-only textbox.
I´ve tried:

Dim nazovsuboru As String = IO.Path.GetFileNameWithoutExtension(InputFile.Text)
Private Sub Button5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button5.Click
        MsgBox(nazovsuboru)
    End Sub

Error: An error occurred creating the form. See Exception.InnerException for details. The error is: Object reference not set to an instance of an object.

I´ve looked at many different solutions, but none of that works for me. Thanks a lot.