What USB do you use, i mean what format it is formatted?
Have you extracted firmware to USB or? FFB searches for fat32 formatted USB and /T-CHU7DEUC/image directories on it. If not found - then gives error. Please check if you have done all according manual
Solution to your problem:
Pls download FFB
once again, remove game from TV (select SamyGO Horse - remove all), then attach new downloaded FFB and copy to TV.