Owncloud StorageNotAvailableException intermittent failures

I have installed two univention servers with the owncloud application. Client files are stored on a Netgear ReadyNAS.
I have detected that the owncloud windows clients (Client version 2.7.6) show errors: “error transfering https_://IP/owncloud/remote.php/dav/files/USER/FOLDER/ - server replied:Service unavailble”
On server logs show:
“Storage smb::USER@IP_NAS//FOLDER//DIRECTORY/ not available”}

When this failure occurs, owncloud clients do not access their folders but after a few seconds they reconnect. It is a temporary error.
The same thing happens from the web browser, access to the folder fails when clicking, but if you try again a little later it works.

In some forum recommended removed the “smbclient” binary and install php-smbclient.

Thank you