I got a friend's TT ONE XL with original map the Western_Europe_1GB.
I wanted to load a new map of Argentina (Argentina_Mapear_865.3302).
When I inserted an empty 2GB SD card to the TT slot, the TT refused to work saying the SD card is not TT-SD card or ... something similar.
Having no other option, I removed some files (from subdirs "voices" and "zip") to free the internal memory and added a new subdir with ...