QNAP NAS Error Code 51: How to Fix It

Easy 20-45 minutes Medium Severity Verified June 2026
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Error Code
51
Brand
QNAP
Product Type
nas
Severity
Medium
DIY Difficulty
Easy
Estimated Fix Time
20-45 minutes
QNAP NAS Error Code 51 indicates that the AFP (Apple Filing Protocol) service on your QNAP device has been deprecated and is no longer supported or recommended for use. Apple itself deprecated AFP in macOS in favor of the more modern SMB (Server Message Block) protocol, and QNAP has followed suit by removing active support for it. This means any Mac clients still connecting via AFP may experience connection failures, reduced performance, or data access issues, and you should migrate to SMB as soon as possible to restore reliable file sharing.
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Tools You'll Need

How to Fix Error Code 51

  1. Log In to QNAP QTS Admin Panel

    Make sure you are logging in over a secure local network. Avoid making these changes over an unsecured public Wi-Fi connection.

  2. Disable the AFP Service on the NAS

    Before disabling AFP, confirm that no critical workflows or users are still actively relying on AFP connections. Abruptly cutting off active sessions could interrupt ongoing file transfers.

  3. Enable and Configure SMB Service

    Do not enable SMB1 as it has known security vulnerabilities (e.g., it was exploited by the WannaCry ransomware). Use SMB2 or SMB3 only.

  4. Update Shared Folder Permissions for SMB

  5. Reconnect Mac Clients Using SMB

  6. Update QNAP Firmware to the Latest Version

    Back up all NAS data before performing a firmware update. While firmware updates are generally safe, unexpected power loss during an update can cause system issues. Ensure the NAS is connected to a reliable power source or a UPS (Uninterruptible Power Supply).

  7. Verify the Error Code 51 Is Cleared

    Restarting the NAS will briefly interrupt access to all shared folders and running applications. Notify users before restarting during business hours.
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When to Call a Professional

Contact QNAP technical support or a qualified IT professional if: (1) you cannot log in to the QTS admin panel, (2) disabling AFP causes critical business services to fail and you are unsure how to migrate them, (3) the error persists after all steps and a full firmware reinstall, or (4) your NAS is part of a larger enterprise network with Active Directory or LDAP integration that requires professional reconfiguration of SMB permissions.

Frequently Asked Questions

What does QNAP Error Code 51 mean?
QNAP Error Code 51 means the AFP (Apple Filing Protocol) service on your NAS has been deprecated. AFP is an older file-sharing protocol originally designed for Apple devices that is no longer actively supported by Apple or QNAP. You should migrate to SMB (Server Message Block) protocol instead.
Will disabling AFP on my QNAP NAS cause me to lose any data?
No. Disabling AFP only removes the method by which Mac clients connect to the NAS using the AFP protocol. Your data stored on the NAS remains completely intact. You simply need to reconnect your Mac clients using SMB instead of AFP to continue accessing your files.
Can modern Macs still connect to a QNAP NAS without AFP?
Yes, absolutely. macOS 10.9 (Mavericks) and all later versions natively support SMB3, which is faster, more secure, and fully compatible with QNAP NAS devices. Most users actually experience better performance after switching from AFP to SMB.
How do I connect my Mac to a QNAP NAS using SMB?
On your Mac, open Finder, click 'Go' in the menu bar, then 'Connect to Server' (or press Cmd+K). Type 'smb://[your NAS IP address]' (for example, smb://192.168.1.100) into the address field and click 'Connect'. Enter your QNAP username and password when prompted, then select the shared folder you want to mount.
Why did QNAP deprecate the AFP service?
QNAP deprecated AFP because Apple itself stopped actively developing and recommending AFP starting with macOS High Sierra (2017) and officially removed AFP client support in macOS Ventura (2022). SMB is now the industry standard for file sharing across Windows, macOS, and Linux, offering better performance, stronger security, and broader compatibility, making AFP redundant and unnecessary.

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