I assume you have this error message on the screen because you exported the song(s) to subfolder. By default the uTrack try to load the songs from the root folder if you have no songs there you can see this error message. This only happens if you have pre-loading enabled (pre recording disabled) and the exported songs located in subfolder.
Actually you will not see this message if you browse the folder where you exported your songs the preloading should succeed.
We will correct this “issue” with the coming firmware release