Summary
The Windows 11 Feb update (KB5077181) locks some Samsung PCs out of C: with a “C:\ is not accessible” error.
Microsoft confirms Galaxy Book 4 and other Samsung models affected; the Samsung Share app is suspected but unconfirmed.
Some suggest changing C: permissions, but fixes are risky—uninstall the update or wait for a Microsoft patch if you want to play it safe.
Windows 11 has been having an awful time with updates recently. In January, it felt like a week hadn’t gone by without something going wrong. While February seemed a little quiet, it seems the trend of strange Windows 11 bugs has continued into March. Microsoft has confirmed that some Samsung devices are getting a “C:\ is not accessible – Access denied” error after installing the latest Windows 11 updates.
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Some Samsung devices cannot find their C: drives after the February Windows 11 update
There are some user-suggested fixes, but they may be risky
As spotted by Neowin, Microsoft has updated its “Windows 11, version 25H2 known issues and notifications” page. This is where Microsoft posts any new information on critical bugs and issues to keep everyone updated on what the company is working on.
Recently, Microsoft added the following text to the March 2026 issues section:
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. 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 notes that the issue seems to be an international problem, affecting “[the] Samsung Galaxy Book 4 and other Samsung consumer devices.” Microsoft suspects it has something to do with Samsung Share, but it’s not sure yet.
Meanwhile, people are flocking to a Reddit thread discussing the issue. Three people in that thread have said that logging into an administrator account, right-clicking the C: drive, going into its properties, clicking the Security tab, then giving the user permission to use the C: drive. The fix may cause issues, so if you’re a little concerned, it’s probably best to delete the update or wait for a patch.