this is an old thread but in gnome bug reports it is a recent open issue so it may be of some use to anyone searching for hours for a solution to fix gvfs-fuser issues - which all seem to be tightly related.
Error Msg from meld:
Error copying '/media/root/5FDA03906F33F217/SAVE/rsyncTEST-usb/allusers' to '/run/user/0/gvfs/ftp:host=192.168.0.103/var/ftp/ftpd/images/PersistenceUSBs/rsync-meld/allusers' [Errno 95] Operation not supported: '/run/user/0/gvfs/ftp:host=192.168.0.103/var/ftp/ftpd/images/PersistenceUSBs/rsync-meld/allusers'.
I encountered the gvfs-fuser issue attempting to use meld/diff/kdiff over ftp. Seems the problem is between fuser and gvfs. The problem seems not to occur in 3.15.1 but begins being reported in 3.15.2.(the new python ver?) Solution is a workaround not a fix - files/directories will copy but error is still displayed.
Salute Christopher for defining the problem and providing the SOLUTION: https://unix.stackexchange.com/a/77457
All other solutions, related bug reports, and versions of the gvfs-fuser bug are HERE due to rules on 2+ links from newer members (though it seems logical to want newbies to post supporting links since often newbie questions are vague although problems newbies encounter are common throughout the web...)