When I try to import songs to a folder in SDExplorer I get a NoGo sign
Technics' file system allows maximal 20 songs per folder and maximal 99 folders per SD-Card. So suppose you have 10 songs in a folder and you try to add 12 songs, you get "nogo" you can import a set of 10 songs to that folder.
The same holds for reshuffling songs on an SD Card. However the chance of 'surprise' is less evident. I can imagine that you download songs from internet, e.g. from the Technics KN7000 site, and then put them in a folder. You think you added 20 songs, but because every song consists of a different number and set of files. So 'select all' and then import will make clear by the Nogo-sign that you try to import more than 20 songs.