Windows 11 KB5074109 OneDrive and Dropbox Files Not Opening

What is the KB5074109 cloud storage bug?

After installing the Windows 11 January 2026 cumulative update (KB5074109), applications freeze or become unresponsive when opening or saving files stored in cloud-backed storage like OneDrive or Dropbox. Microsoft officially acknowledged this regression: apps work normally until you try to perform a file operation on a cloud-synced folder, at which point they hang indefinitely. Outlook is especially affected when PST files are stored in OneDrive, often requiring Task Manager to terminate the frozen process.

This bug affects Windows 11 versions 25H2, 24H2 (KB5074109), and 23H2 (KB5073455). Microsoft released an emergency out-of-band fix on January 24, 2026 — KB5078127 for 24H2/25H2 and KB5078132 for 23H2.

When does it occur?

• When opening a document from OneDrive or Dropbox in any application (Word, Excel, Notepad, etc.)
• When saving or "Save As" to a OneDrive or Dropbox-synced folder
• When Outlook accesses a PST file stored on OneDrive — Outlook hangs and won't reopen until terminated
• When Adobe InDesign saves to a cloud-synced location (triggers InDesign Error 2)
• When any application performs file I/O on a cloud-backed folder after the January 13, 2026 update
• When previously downloaded emails re-download in Outlook after the update

Common causes

• KB5074109 (January 13, 2026) introduced a regression in Windows' file I/O handling for cloud-synced folders
• The bug affects how Windows interacts with cloud storage providers' file system integration layer
• OneDrive's on-demand file hydration triggers the hang when apps request file access
• Dropbox's Smart Sync feature encounters the same file system regression
• Outlook PST files on OneDrive are particularly vulnerable because Outlook keeps persistent file locks
• The same regression exists in KB5073455 for Windows 11 23H2
• Google Drive and other cloud providers using similar file system hooks may also be affected

Step-by-step fixes

1. Install the out-of-band fix KB5078127 — Go to Settings > Windows Update > Check for updates. Download and install KB5078127 (for Windows 11 24H2/25H2) or KB5078132 (for 23H2). This is Microsoft's official fix released January 24, 2026. If the update doesn't appear, enable "Get the latest updates as soon as they're available" in Windows Update settings.

1. Download from Microsoft Update Catalog — If KB5078127 doesn't appear in Windows Update, download it manually from the Microsoft Update Catalog at catalog.update.microsoft.com. Search for "KB5078127", download the version matching your architecture (x64 or ARM64), and install the .msu file manually.

1. Move PST files off OneDrive (Outlook workaround) — If Outlook is freezing, move your PST files from OneDrive to a local folder. Open File Explorer, navigate to your OneDrive folder, find any .pst files, and move them to C:\Users\YourName\Documents\Outlook Files\. Then in Outlook, go to File > Account Settings > Data Files and update the file path to the new local location.

1. Pause cloud sync temporarily — As a temporary workaround, pause OneDrive sync: click the OneDrive icon in the system tray > Settings gear > Pause syncing > 24 hours. For Dropbox, click the Dropbox icon in the system tray > your avatar > Pause syncing. This allows applications to access local cached copies without triggering the file system hang.

1. Save locally, then sync — Change your default save location to a local folder that is not synced to any cloud provider. In Office apps, go to File > Options > Save and change the default local file location. Save your work locally first, then copy or move files to cloud folders when ready.

1. Uninstall KB5074109 if KB5078127 is unavailable — Open Settings > Windows Update > Update history > Uninstall updates. Find "2026-01 Security Update (KB5074109)" and click Uninstall. Alternatively, run wusa.exe /uninstall /kb:5074109 from an elevated Command Prompt. Note: some users report error 0x800f0905 blocking the uninstall — if this happens, install KB5078127 instead.

1. Known Issue Rollback for enterprise (Group Policy) — For IT administrators: Microsoft provides a Known Issue Rollback (KIR) policy that disables only the specific change causing the regression while preserving other security fixes. Download the KIR policy definition from Microsoft, install it, then configure it via Local Group Policy Editor under Computer Configuration > Administrative Templates.

1. Force terminate frozen applications — If an application is currently frozen, press Ctrl+Shift+Esc to open Task Manager, find the unresponsive application, right-click it, and select "End task." Restarting the application after installing KB5078127 should resolve the freeze.

If it still doesn't work

If the issue persists after installing KB5078127, verify the update installed correctly: go to Settings > Windows Update > Update history and confirm KB5078127 appears in the list. If OneDrive itself is behaving erratically, try resetting it: press Win+R, type %localappdata%\Microsoft\OneDrive\onedrive.exe /reset and press Enter. OneDrive will restart and re-sync. For Dropbox, try uninstalling and reinstalling the desktop client. If you're in an enterprise environment with managed update policies, contact your IT department about deploying the KIR policy or KB5078127 via WSUS or SCCM. Microsoft's February 2026 Patch Tuesday update is expected to include the cloud storage fix in the standard cumulative update.