<input type="file" name="ctl00$ContentPlaceHolderContent$FileUpload_opfFile" id="ctl00_ContentPlaceHolderContent_FileUpload_opfFile" style="width:406px;" />
This is the source html tag
Using IE9 the SetValue method worked for that tag when I changed the type to "text".
With type="file" I get a "Could not start AutoItX3 Control through OLE" error.
It could be a security issue.