Microsoft has confirmed a serious bug affecting some Windows 11 PCs that can block access to the system’s C: drive.
This can potentially prevent apps from launching and everyday tasks from working properly.
The issue appears after installing the February 2026 Patch Tuesday update (KB5077181) and later updates. On affected machines, users may see an error message stating “C: is not accessible – Access denied.” While that might sound like a simple file permission issue, Microsoft says the consequences can be much broader.
Because the system drive becomes inaccessible, some applications may fail to start altogether. Reports suggest this can include tools such as Outlook, web browsers, system utilities and other common programs. In practical terms, that can leave a PC severely limited. As a result, users are unable to open files, run apps or perform administrative actions.
Does it affect every Windows 11 device?
The good news is that the bug does not appear to affect every Windows 11 device. According to Microsoft, it is primarily showing up on certain Samsung laptops, particularly models in the Galaxy Book4 line. Reports have surfaced from users in regions including Brazil, Portugal, South Korea and India.
Microsoft believes the issue may be linked to the Samsung Share application. However, the company says the root cause hasn’t been fully confirmed yet. The bug only appears to impact systems running Windows 11 versions 24H2 and 25H2. This means older builds, as well as Windows 10 should remain unaffected.
For now, Microsoft says it is actively investigating the problem. Some users online have suggested workarounds such as manually changing drive ownership permissions. However, that approach carries risks and isn’t recommended unless absolutely necessary.
If your device is affected and rolling back the update doesn’t resolve the issue, the safest option may simply be to wait for Microsoft to release an official fix. Until then, the bug serves as another reminder that even routine security updates can occasionally bring unexpected headaches.
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