error: Object reference not set to an instance of an object.

Hello,

I'm trying to make a map editor so I need to give my map data. But when I try to read/write the data I'll get an error
"Object reference not set to an instance of an object." I won't get a message box what tells me '1'.

Code:

---

    Private Sub ToolStripButton1_Click(sender As System.Object, e As System.EventArgs) Handles ToolStripButton1.Click
        Dim m As New Map
        m.Layer.Ground.Tile(5, 5).Data = 1
        MsgBox(m.Layer.Ground.Tile(5, 5).Data.ToString)
    End Sub

---

Code:

---

Public Class Map

    Public Layer As Layerrec

    Public Structure Layerrec

        Public Ground As Layer

    End Structure


End Class

---

Code:

---

Public Class Layer

    Public Tile(10, 10) As Tile

End Class

---

Code:

---

Public Class Tile

    Public Data As Integer


End Class

---

what am I doing wrong?

Your classes don't make any sense at all. In Map you have a circular definition and a structure that consists of only one variable. In Tile you have a single variable but everywhere else refer to Tile as defined by two parameters. And what's happening in Layer is beyond me entirely. With the best will in the world you really don't know what you're doing, do you? This may help http://www.homeandlearn.co.uk/net/nets11p5.html although I suspect that you actually need a much more thorough grounding in the use of classes altogether.