It appears to be a security issue. Go to a command line and try this command:
mount -t cifs -o rw,nounix,iocharset=utf8,_netdev,file_mode=0777,dir_mode=0777,sec=ntlm,username=guest,password=******* '//daisy/Movies' '/mnt/disks/daisy_Movies'
Change the credentials to your actual credentials. UD changes the password to '*'s to hide the password in the log. Let me know if it mounts the smb share.
I added 'sec=ntlm' that is an older security mode for the credentials and used to be the default. The new default is 'sec=ntlmssp' and your NAS is probably using the older method.
EDIT: The test I asked you to do is not as straight forward as I thought. I will release a new version of UD today that will try to remount the device with the 'sec=ntlm' if the mount with the default fails. Update UD and then try your mount again and post the UD log entries if it fails.