Add this line to force legacy PnP handling:
Open the Windows Start Menu and search for . Navigate to Device Security on the left-hand menu. Click on Core isolation details . Toggle Memory integrity to Off . Restart your computer to apply changes.
After applying these fixes, check the again. The "Virtual USB Bus" should appear under "System devices" or "USB controllers" without any warning icons.
setting. This feature prevents drivers that do not meet strict security standards from loading. Matsusada Precision How to Fix Windows Security from the Start menu. Navigate to Device Security Core isolation details Memory integrity Restart your computer to apply the changes. Matsusada Precision Alternative Solution: Registry Modification mastercam+x72022+virtual+usb+bus+error+39+fixed
The splash screen appeared. Then the license check. Then—the toolpath workspace.
Uninstall the existing from the Device Manager.
Is your driver showing up under or Universal Serial Bus Controllers ? Add this line to force legacy PnP handling:
The core issue is that Windows 10 and 11 have stricter security protocols—specifically and Driver Signature Enforcement —which block older virtual USB bus drivers from loading.
In older environments, Mastercam relied heavily on virtual USB bus drivers (such as MultiKey) to emulate hardware locks or manage HASP network licenses. On newer versions of Windows 10 and Windows 11, Microsoft enforced strict security protocols that break compatibility with these legacy emulator tools. The two primary triggers for Error 39 are:
This is the most frequent and effective resolution. Open the Windows Security app. Navigate to Device Security > Core isolation details . Toggle Memory integrity to Off . Restart your computer for changes to take effect. Toggle Memory integrity to Off
Method 2: Delete Corrupted Registry UpperFilters/LowerFilters
Some Windows security updates (like KB5004298) can cause issues with virtual keys. If the error appeared suddenly, uninstalling recent security updates might fix it. Summary of Fixes Error 39 in Device Manager Core Isolation blocks unsigned driver Disable Memory Integrity Driver fails to load Corrupted Registry Keys Delete Upper/Lower Filters Virtual USB failed to install Driver Signature Enforcement Disable Signature Enforcement Conclusion
Mastercam users transitioning from older versions like to modern releases like 2022 often encounter the frustrating "Virtual USB Bus Error 39" . This error typically presents as a yellow exclamation mark in the Device Manager next to the "Virtual USB MultiKey" or "Sentinel" driver, preventing the software from detecting the necessary security dongle.