Object reference not set to an instance of an object

Dear all

I am totally new to ASP.NET and I am trying to follow some examples from a book I have bought. However i have encountered the following error:-

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:


Line 56: strPanelName = "pnlForm" & ViewState("CurrentPage")
Line 57: pnlPanel = FindControl(strPanelName)
Line 58: pnlPanel.Visible = True
Line 59:
Line 60: End Sub


Source File: C:\Inetpub\wwwroot\JohHidingContent\PanelMultiPage .aspx.vb Line: 58

Here is my code for this section:-

Sub btnNextPage_Click(ByVal s As Object, ByVal e As EventArgs)

Dim pnlPanel As Panel
Dim strPanelName As String

'Hide Previous Panel
strPanelName = "pnlForm" & ViewState("CurrentPage")
pnlPanel = FindControl(strPanelName)
pnlPanel.Visible = False

'Show current Panel
ViewState("CurrentPage") += 1
strPanelName = "pnlForm" & ViewState("CurrentPage")
pnlPanel = FindControl(strPanelName)
pnlPanel.Visible = True

End Sub

Can you please help me out?

Thanks

OK I found the error, I forgo to declare it in the HTML

Thanks