I've been battling with Cobian Backup 11's persistent refusal to create directories on my Synology DS412 NAS, despite having proper credentials configured. Here's what I've discovered through extensive testing on both Windows XP SP3 and Windows 7 x64 systems.

The key insight came when examining how Windows services interact with network resources. Even when running under an administrator account, services operate in a different security context than interactive logins. Here's the proper way to configure the service:

sc config "Cobian Backup 11" obj= "DOMAIN\username" password= "yourpassword"

However, simply setting this isn't enough - you need to ensure the account has explicit permissions on both ends.

On the Synology side, these settings proved critical:

• Enable SMB3 protocol (maximum compatibility mode)
• Set "Enable NTLMv1 authentication" if using older Windows versions
• Explicitly grant permissions to the service account in both DSM and the share ACLs

To verify the service can actually access the share, I created this PowerShell test script:

# Test network access as service account
$cred = Get-Credential
Invoke-Command -ComputerName localhost -Credential $cred -ScriptBlock {
    Test-Path "\\nas1\backups"
    New-Item -ItemType Directory -Path "\\nas1\backups\test" -Force
}

Windows services run in session 0 isolation, which means they don't inherit your interactive login's network credentials. The definitive solution was to:

1. Map the network drive persistently using the service account:

net use Z: \\nas1\backups /persistent:yes /user:nasusername password

2. Configure Cobian to use the mapped drive (Z:\foo\bar) instead of UNC path

For environments where drive mapping isn't feasible, storing credentials in Windows Credential Manager works well:

cmdkey /add:nas1 /user:nasusername /pass:password

This allows the service to authenticate without hardcoding credentials in configuration files.

When Cobian Backup (v11) runs as a service on Windows machines (XP SP3/Win7 x64) targeting a Synology NAS share, it fails with:

Error: "Couldn't create the destination directory \\\\nas1\\backups\\foo\\bar\\: 
The filename, directory name, or volume label syntax is incorrect"

Despite:

• Running Cobian service under admin credentials
• Manually verifying share accessibility via Explorer
• Pre-creating destination folders
• Setting anonymous NAS access

The backup still fails - indicating deeper authentication issues.

Key difference: Windows services can't access network resources using your interactive credentials due to security restrictions.

Method 1: Stored Credentials (Recommended)

@echo off
cmdkey /add:nas1 /user:YOURDOMAIN\username /pass:yourpassword
net use \\nas1\backups /persistent:yes

Method 2: Service Configuration

Edit Cobian service properties:

1. services.msc → CobianBackup → Properties
2. Log On → "This account" → Enter NAS credentials
3. Grant "Log on as a service" rights via secpol.msc

Filter for:

Process Name: cbService.exe
Result: ACCESS DENIED
Path: \\nas1

For complex environments:

robocopy C:\\source \\\\nas1\\backups /MIR /Z /R:1 /W:1 /TEE /LOG+:backup.log
net stop CobianBackup
net start CobianBackup

• Enable NTLMv1 in Control Panel → File Services → SMB
• Create dedicated backup user with explicit share permissions
• Disable "Windows ACL" feature temporarily for testing