Oops, I had wrong version, v1.11b04 is the transitional version used before v1.20 which is included in the .zip file for v1.20.
I would give the process a try again, doing a factory reset and apply v1.11B04 then apply v1.20 using FF browser for Windows. Then do a factory reset. While the router resets, clear the FF browser caches, exit the browser then relaunch and set up the router from scratch. Do not load any saved config files.
Let us know how it goes...