Microsoft recently released a major security update that addressed several issues and flaws in Windows 11. However, some users who have installed the vital patch are now suffering from a crippling bug that is leaving them blocked from files and unable to launch certain applications, including Microsoft Outlook, Office apps and certain web browsers.

The error appears to be blocking access to the C drive on PCs with those affected seeing the message “C:is not accessible – Access denied.”

It’s clearly a nightmare for anyone unlucky enough to have been hit by this gremlin, but not everyone is suffering from it. It’s been confirmed that PCs made by Samsung, including the Galaxy Book 4, are on the hit list.

The highly annoying issue impacts a number of Samsung Galaxy Book 4 laptops and Samsung Desktop models. These are thought to include devices with following model numbers: NP750XGJ, NP750XGL, NP754XGJ, NP754XFG, NP754XGK, DM500SGA, DM500TDA, DM500TGA, and DM501SGA.

“Microsoft has received reports of an issue in which some Samsung device models lose access to the C: drive after installing the February 2026 security update (KB5077181) and subsequent updates,” Microsoft confirmed.

“Users might encounter the error, “C: is not accessible – Access denied”, which prevents access to files and blocks the launch of some applications including Outlook, Office apps, web browsers, system utilities and Quick Assist.

“Affected devices encounter the issue when users execute common actions, such as accessing files, launching applications, or performing administrative tasks, and do not require any specific user action beyond routine operations. In some cases, users are also unable to elevate privileges, uninstall updates, or collect logs due to permission failures.”

Microsoft says the issue has been reported across the world, including Europe, Brazil and India.

The US firm’s latest investigations indicate that the issue may be related to the Samsung Share application, though the root cause has not yet been fully validated.

It’s unclear when a fix will be rolled out but if you own a Samsung PC and haven’t updated to Windows 11 versions 24H2 and 25H2 to might be a good idea to wait.

Those still on Windows 11 versions 24H2 and 25H2 would be wise to stay put.