Using createDocumentFromUrl causes an exception

I have written a small application using VB2010 express. This app uses createDocumentFromUrl to retrieve a web page into a HTML DOM object. The code is as follows:

Dim oMSHTML As New mshtml.HTMLDocument
Dim oThumbDocument As mshtml.HTMLDocument

oThumbDocument = oMSHTML.createDocumentFromUrl(txtSingleItemAW.Text, vbNullString)

I have VB2010 express installed on two machines, one running Windows 7 64bit and the other is Vista 32bit. I am (obviously) compiling this code separately for each machine.

The problem I am having is this and it is identical for both machines: When the createDocumentFromUrl line is executed I get a "An unhandled exception of type 'System.AccessViolationException' occurred in mscorlib.dll". It happens in both a debug session and a compiled executable. I have not made any changes to the code for over two months.

I wrote the code approx. 6 months ago and it has been running perfectly since then until last week. It seems that it may have something to do with Windows Update which was done shortly before running the app. on both machines.

Can anyone help please?