The June 2026 cumulative update for Windows 11, KB5094126 (Build 26200.8655), is causing serious problems on a slice of machines. Some PCs refuse to boot after installing it, throwing a black screen with error 0xc0430001 or dropping into BitLocker recovery, while others lose the ability to open OneDrive from File Explorer. The trouble clusters heavily around HP business hardware, but it is not limited to one model.
Quick answer: If your PC will not boot after KB5094126, enter BIOS, temporarily disable Secure Boot, return to Windows, let the update finish installing, then re-enable Secure Boot. If OneDrive no longer opens from File Explorer, sign in with a Microsoft account and turn User Account Control back on.
KB5094126 boot failures and 0xc0430001 BSOD on HP and Dell PCs
The most damaging fault hits at startup. After deploying KB5094126, affected devices either fail to load Windows entirely or demand a BitLocker recovery key on every restart. The black screen typically carries error code 0xc0430001, and some machines fall into a reboot or recovery loop that does not clear even after the key is entered. A few users also report a DPC_WATCHDOG_VIOLATION boot loop that only resolves once the update is removed.
HP systems dominate the reports, with one administrator managing hundreds of HP machines seeing most of them stall after the rollout. The models showing up most often are listed below.
| Vendor | Affected models reported |
|---|---|
| HP | EliteBook 840 G10, ProBook 460 G11 / 460 G11, Engage One Pro 15.6 G2 AiO POS, ZBook |
| Dell | Precision, Precision 7530 |
Owning one of these models does not guarantee a problem. The failure depends on the interaction between the update and the firmware on each machine, so identical hardware can behave differently depending on its BIOS version and partition layout.
Why KB5094126 stops some PCs from booting
KB5094126 turns on the Secure Boot certificate update for most supported PCs, and the update touches Secure Boot certificates, Boot Manager, and EFI contents. On machines with a small EFI System Partition, often the older 100MB layout rather than a newer 500MB to 1GB partition, Windows cannot write the files it needs. When that write fails, Secure Boot blocks Windows from loading, which produces the black screen with 0xc0430001, and BitLocker-protected systems get sent to the recovery key prompt.
HP devices are more exposed because HP stores firmware recovery files under the EFI partition, in locations such as EFI\HP\DEVFW, which can eat up the limited space. The root cause is usually a small or crowded EFI partition combined with an outdated BIOS, not the SSD or the Windows install itself. If you can boot into the desktop, open Event Viewer and look for TPM-WMI errors. A telling one reads, “The secure boot update failed to update Boot Manager (2023) due to the error: insufficient disk space.”
Note: For machines reinstalled from custom images, the failure can come from a missing boot.stl file on the installation media. Secure Boot uses this file to verify that boot files are trusted, and it must match the same Windows version and architecture. Using the Update WinPE script handles this automatically, or you can copy boot.stl from the Windows\Boot\EFI folder of a working Windows device into the matching folder on your media.
Fix a PC that will not boot after KB5094126
Disabling Secure Boot temporarily is the workaround that has restored boot on every affected machine. Before you start, make sure you can retrieve your BitLocker recovery key.
You know the fix worked when the machine boots straight to the desktop without the black screen or a BitLocker prompt, and the June 2026 update shows as installed in Windows Update. If the device still struggles, update the BIOS/UEFI to the latest version and check free space in the EFI partition, resizing it if it is full. Where none of that helps, leave Secure Boot off until HP or Microsoft addresses the firmware mismatch.
Fix OneDrive not opening in File Explorer after KB5094126
On some PCs, KB5094126 breaks the cloud storage shell integration in File Explorer. After the update, clicking OneDrive in the left pane, the tray icon, or an existing shortcut does nothing, and the folder never opens. Dropbox and iCloud Drive can hit the same wall, though far less often than OneDrive.
Your files are not lost. If you browse manually to C:\Users\username and open the cloud folders directly, they load normally. The breakage only affects the common route through the File Explorer sidebar or the system tray icon.
The trigger is a conflict involving User Account Control. The problem appears on systems where UAC is disabled, and the signed-in user is a local administrator. Turning UAC back on restores the integration even with KB5094126 still installed.
To get cloud folders working from Explorer again, switch to a Microsoft account and enable UAC. After that, OneDrive opens from the sidebar and tray as it did before. If you cannot change those settings, removing KB5094126 also restores access while you wait for a fix.
KB5094126 breaks Word integration in business apps
A separate confirmed bug affects line-of-business software that relies on Microsoft Word. Word still opens documents on its own, but applications that embed Word, automate it, or open Word files inside their own document systems are failing after the update. This shows up in dental, accounting, and other specialized software.
The applications reported with this fault include the following.
- Dentrix
- Softdent
- CCH ProSystem fx Engagement
- CCH ProSystem fx Workpaper Manager
- Older Eaglesoft / SmartDoc
- Neurology software that uses Word
If your workflow depends on one of these tools, removing KB5094126 restores the Word integration until a patched build arrives.
KB5094126 remains an important security release that closes around 200 flaws, including five zero-days, so it should still be installed once your machine is stable. The update installs automatically unless you deferred it before download, and its full notes live on the Microsoft support page for KB5094126. Microsoft has not yet publicly acknowledged the boot, OneDrive, or Word problems, so watch the update history if you manage HP or Dell fleets and stage the rollout to a test group before deploying it widely.
