I really have no explanation for that. I will say one thing though, there really is no reason for that code to not be in the form itself. The code is specific to that form because it's referring directly to that form, so it should be in that form. Organising your code is good but you're over-organising for no gain. I would just try moving that code into the form itself and see if that makes any difference. I'm not sure that it will but I think that it's worth a try. I just tried this and it worked for me:
vb.net Code:
Private Sub Form1_Shown(sender As Object, e As System.EventArgs) Handles Me.Shown
Dim filePath = Path.Combine(Application.StartupPath, "HTMLPage1.htm")
Dim fileContents =
File.
ReadAllText(filePath
)
RichTextBox1.Text = fileContents
WebBrowser1.DocumentText = fileContents
End Sub