Nothing on your NAS changed. Nothing on your network changed. Windows changed - twice, in one update - and your guest share was standing exactly where the walls went up.
This is now one of the most common sharing complaints there is: the home NAS, the router's USB drive, the old file PC - all reached happily for years - and then Windows 11 updated to version 24H2 and the same double-click produces the guest access error. Microsoft announced both changes openly, in advance, as security work. Knowing exactly which two changes landed tells you exactly which fix applies to your device - and why the permanent repair is not another workaround, but the password the share should have had all along.
Summary of Microsoft's published 24H2 SMB changes. The last row is the clue to the whole fix: authenticated shares sailed through untouched.
0x80070035, which means the device was not found and points at the network insteadTwo out of three, and you can proceed with confidence. All three, and it is certain.
SMB signing stamps every packet with proof it came from the real session, which kills tampering and relay attacks. It existed in Windows for thirty years as an option; 24H2 made it required by default on all connections, for Windows 11 and Windows Server 2025 alike. The catch for old devices: signing needs the key material from a real login. A guest session has none, so a guest connection cannot be signed, and a client that requires signing must refuse it. Microsoft's own guidance is explicit that guest logons do not support signing even when the client allows guest logons - which is why, on 24H2, re-allowing guest alone sometimes changes nothing.
The second change closed a quieter behaviour: when a login failed, Windows would silently fall back to trying guest. Enterprise editions lost that fallback back in Windows 10 version 1709, but Home and Pro kept it for years - which is why so many guest shares worked without anyone ever configuring them. Windows 11 Pro now refuses guest credentials by default. If your share sort of worked through a failed login that fell back to guest, 24H2 ended that arrangement.
Watch the video for the fix in action, and use this page to understand which of the two 24H2 changes is blocking your share.
▶️ Watch Full VideoPartly, and probably not for long. The guest fallback change hit the Pro edition first, and editions have been converging on the same defaults for years. Treat a still-working guest share on any edition as borrowed time, and set up the account while it is convenient rather than urgent.
No. Authentication is the direction Windows is moving toward, not away from. Shares with real logins were untouched by 24H2 and are what every change is designed to encourage. The fixes that break are always the ones that switch protections off.
Feature updates can be rolled back only briefly, and staying behind means missing every security patch that follows. You would be freezing your PC in a weaker state to protect a folder-sharing habit that takes five minutes to fix properly. The ladder above is shorter than the rollback dance.