MyBase.Render outputs to the browser for unknown reasons

-using asp.net 1.1

I am trying to make some replacements in html before it is rendered. Unfortunately just capturing the html seems to cause a "1" to be output to the browser. Here is the code I use to do this up to the grabbing of the text which cause the output:

Protected Overrides Sub Render(ByVal writer As System.Web.UI.HtmlTextWriter)

Dim sw As New System.IO.StringWriter
Dim hw As New HtmlTextWriter(sw)
MyBase.Render(hw) 

This code works on all the test applications I've created, but in the project I need to add it into if I put just this code it will prefix the number 1 before any of my html which I would output (after mod ...