Windows April Update KB5083769 blocks VSS
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- Joined: 10 May 2026
April update has caused VSS to hang when trying to do a backup of locked files. According to many articles on line (e.g. https://www.notebookcheck.net/Windows-11-KB5083769-is-breaking-Acronis-Macrium-and-other-backup-apps.1289937.0.html), Microsoft has added a driver to the vulnerable driver list that interferes with FFS use of VSS. Does anyone have a solution or will there be an update to solve this? I am on version 14.9 - 64 bit. Obvious workaround is to shut down programs like Outlook that have locked files, so that the backup can be done without VSS. But am hoping for a better solution.
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The blocked kernel driver ist psmounterex.sys, created by Paramount Software UK for Macrium Reflect. If this affects FFS's use of Volume Shadow copy, the workaround would be to either uninstall Macrium and their kernel driver, or update to their latest version which apparently is not affected by Microsoft's block.
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- Joined: 10 May 2026
Some further information. I have 2 Dell desktops (2021 Intel core i9 and 2025 core Ultra7). Shortly after the Microsoft Update, both had the same problem with FFS using VSS. Interestingly, after a few days the problem went away on the older machine but it has persisted on the newer machine. I am using the temporary workaround of shutting down Outlook during backup.
Thanks for your suggestion. I have never had any Macrium products on either machine. I checked in Drivers and DriverRepository folders on both machines and find no trace of psmounterex.sys. Is it possible that there is another driver used by FFS that has been banned? Is the timing with the MS update just coincidence, although it doesn’t seem likely that it would happen on both machines at the same time, shortly after an update on both machines?
Thanks for your suggestion. I have never had any Macrium products on either machine. I checked in Drivers and DriverRepository folders on both machines and find no trace of psmounterex.sys. Is it possible that there is another driver used by FFS that has been banned? Is the timing with the MS update just coincidence, although it doesn’t seem likely that it would happen on both machines at the same time, shortly after an update on both machines?
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you can use
to find out what other VSS providers are installed on your system. Quite possible you find another one blocked by KB5083769.
vssadmin list providers
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- Joined: 10 May 2026
Thanks for directing me towards using vssadmin.
‘List providers’ shows Microsoft as the only provider.
‘List writers’ would hang indefinitely.
Following an Internet tip, I restarted the COM+ Event System service which helped.
‘List providers’ now showed none.
After restarting COM+ Event System, now instead of being stuck on VSS, FFS shows an error:
The Volume Shadow Copy Service could not create a snapshot of "C:\Users\...\....pst". VSS_E_WRITER_INFRASTRUCTURE: An error was detected in the Volume Shadow Copy Service (VSS).
Before I could follow this any further, patch Tuesday arrived, and after May updates, backups are working again as before. So, looks like in May, MS has fixed something that they broke in VSS in April.
‘List providers’ shows Microsoft as the only provider.
‘List writers’ would hang indefinitely.
Following an Internet tip, I restarted the COM+ Event System service which helped.
‘List providers’ now showed none.
After restarting COM+ Event System, now instead of being stuck on VSS, FFS shows an error:
The Volume Shadow Copy Service could not create a snapshot of "C:\Users\...\....pst". VSS_E_WRITER_INFRASTRUCTURE: An error was detected in the Volume Shadow Copy Service (VSS).
Before I could follow this any further, patch Tuesday arrived, and after May updates, backups are working again as before. So, looks like in May, MS has fixed something that they broke in VSS in April.
