I made a few changes (included the "Command line arguements"). Now the code is:

In frmMain (The main/ Startup form):

Code:
    Public Sub CheckAssociation()
        My.Computer.Registry.ClassesRoot.CreateSubKey(".tbx").SetValue("", "Tiny Toolbox", Microsoft.Win32.RegistryValueKind.String)
        My.Computer.Registry.ClassesRoot.CreateSubKey("Tiny Toolbox\shell\open\command").SetValue("", Application.ExecutablePath & " ""%1"" ", Microsoft.Win32.RegistryValueKind.String)
        My.Computer.Registry.ClassesRoot.CreateSubKey("Tiny Toolbox\DefaultIcon").SetValue("", Application.StartupPath & "\TBX.ico")
    End Sub
When FrmMain is Loaded:

Code:
	CheckAssociation()

        If My.Application.CommandLineArgs.Count > 0 Then
            frmResultsViewer.Show()
        End If


I get this error just before frmResultsViewer is Loaded.

Unhandled exception.
File Format is not valid.


Code:
************** Exception Text **************
System.ArgumentException: File format is not valid.
   at System.Windows.Forms.RichTextBox.StreamIn(Stream data, Int32 flags)
   at System.Windows.Forms.RichTextBox.LoadFile(Stream data, RichTextBoxStreamType fileType)
   at System.Windows.Forms.RichTextBox.LoadFile(String path, RichTextBoxStreamType fileType)
   at DevComponents.DotNetBar.Controls.RichTextBoxEx.LoadFile(String path)
   at Tiny_Toolbox.frmResultsViewer.frmResultsViewer_Load(Object sender, EventArgs e) in C:\Users\AMK\Documents\Visual Studio 2010\Projects\Tiny Toolbox\Tiny Toolbox\frmResultsViewer.vb:line 33
   at System.Windows.Forms.Form.OnLoad(EventArgs e)
   at DevComponents.DotNetBar.RibbonForm.OnLoad(EventArgs e)
   at System.Windows.Forms.Control.CreateControl(Boolean fIgnoreVisible)
   at System.Windows.Forms.Control.CreateControl()
   at System.Windows.Forms.Control.WmShowWindow(Message& m)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.Form.WmShowWindow(Message& m)
   at System.Windows.Forms.Form.WndProc(Message& m)
   at DevComponents.DotNetBar.RibbonForm.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)