ListViewWebPart FilterString isn't working

So I'm dynamically creating a PublishingPage and inserting a ListViewWebPart, it's all fine it points to the right list, but I wanted to filter the data returned by the list. So I used the FilterString property, I read everywhere online and the format was suppose to be:

listViewWebPart.FilterString = "FilterField1=SomeFieldName&FilterValue1=SomeValue"

But when the list is displayed on the page, the filter isn't applied, does anyone have any ideas?

Thanks guys

Winston