Do you mean you are trying to install dashboard version 2.0.14719
You put the $ystemupdate folder on the root of the usb key, not a default.xex
If your box is modded, and you have the lastest version of dashlaunch installed, then you have to rename it to $$ystemupdate.
Only ever install a dash update after installing the hacked version first.
also, the RGH is back in the game