Impossible to create folder/files on NAS share with Dolphin

This morning I log to my NAS as usual with Dolphin,
right-click -> create folder
but I get an error
folder exists! Same problem if I try to create a file.
I can instead drag to copy both files and folders without any problems.
I think the problem is due to some update because it has always worked correctly.
I exclude problems with configuration /updates of NAS because I tried the same procedure with Windows and it works.
By the way if I access to the NAS with Dolphin but with samba protocol instead of ftp protocol I can create folders and files.