Several readers reminded me that there are actually two separate HDT 2.0.6 Updaters - one for any version 2.0.x and a smaller one that just works with 2.0.5. Both can be obtained from FWB's HDT Updater web page.
More generally, FWB's Joel McKinnon writes: "The FWB Software website has just gone through some significant structural changes. For updater links it would be best to link to our Download Center index page. Each product category then links off of this page."