YSMenu seems to run fine when launching it from the flashcard, but it stops with the message "Running fat:/_nds/twloader.nds with 1 parameters". And to answer your second question, my flashcard's sd card is 2 GBNormally after loading "Add Games", after the bottom screen flashes grey, and then it switches to the top screen, the bottom screen will have a blue loading bar.
Does YSMenu normally work on your R4, if regularly in use? Is your flashcard's microSD 2GB or lower?
If so, since I don't own the original R4, I can't help. Sorry.