I would only use 16gb SanDisk class 10 as I did try all sorts of 64gb, 32gb, 128gb, and non worked it alway kept asking for formatting or it would not be able to install the BMW software as mind well in your SD Card only BMW software will be installed and nothing else....So, I tried 16gb and every thing went fine installed BMW software and it did delete all other BWM software files from the main SD Card automatically and now I have 9.7gb empty in my main SD Card and 9gb in SD Card............... Check my post here below regarding this memory issue...
http://pro.autel.com:6688/autelsupport/Diagnostic%20System/27129.jhtml?logoTypeId=94&typeName=MaxiSys