I take it that this is the first time you try to install Rockbox on your Recorder20? Unfortunately my Archos is already set up a bit differently and even if I would test installing with the Rockbox Utility, the result is probably different. (I also have a different player.)
Could you check whether there is a ".rockbox" directory (if you are on a Mac this can be hidden) and a recently changed "ajbrec.ajz" file in the root of your player (the drive your Archos appears when connected to USB)?
Another idea - and just to be sure: is your player a "Recorder 20" with monochrome screen and without radio? I'm not sure but it could be that the Utility is unable to distinguish between the "Recorder (V1)", the "FM-Recorder" and the "V2-Recorder", the latter two look differently than the first. Is the device correctly detected as stated on the "selected device" line, including mount point/drive letter?
P.S.: Your "hoax" thread almost made me want to scratch the reply...