Backup to a Synology NAS with DSM 7.0-41890 fails with:
The credentials for location are not specified
Cause
NTLMv1 authentication is disabled by default in DSM 7.0-41890 (see DSM release notes)
Solution
Enable NTLMv1 authentication on NAS: go to DSM Control Panel > File Services > SMB > Advanced Settings > Others and check Enable NTLMv1 authentication.