Failed to decode JSON string: No error setting privilege for shared folder

Hi, I'm using a Vodafone Station Revolution as modem/router and a raspberry pi 2 as system for OMV.
The router share a smb folder that I mounted using "Remote mount" plugin.
After I added this shared folder to FTP service but the folder doesn't show up in filezilla.
If I try to set "provileges" read/write for user pi on this folder I have an error "Failed to decode JSON string: No error"


Where I made a mistake?