that was the problem!
directory : "root/system" was set as predefined "routes,tracks directory",which probably was not writable.
so i changed to an other directory (sdcard/oruxmaps/vag) and now everything is
moreover, last night, as this didn't work, and i urgently needed to share some recorded tracks and "export as" and "share as" didn't work, the only solution i found was to create a GPSies account, and use "upload to" option.
Many thanks for your great application and for your great support!
Evangelos Gkoumas