Sebastian wrote::dex:,

see if "Hide desktop icons" in 'Configure Desktops > Tools' is enabled for those desktops.

Yes, it was checked ...
I try without checking this option and it works fine Thanks a lot for your help.

Hello :-) This week, I moved from windows 7 to windows 10. Everything was fine, I was happy, birds were singing in the sky ... Yesterday, Windows did some updates and, now, Dexpot is no more able to show my wallpapers (everything is black, even in the preview). I use the very last version of Dexpot ...