Windows security updates frequently turn on "Core Isolation" by default. This security feature actively blocks virtual USB emulators and older sentinel drivers from starting, throwing Error 39. Press the , type Device Security , and hit Enter . Click on Core isolation details . Toggle the Memory integrity switch to Off . Restart your PC for the changes to take effect.
Open Device Manager → Show hidden devices. Under "System devices" appeared with a yellow exclamation. Uninstall it, and check "Delete driver software for this device."
The deeper issue: The HASP driver’s internal DriverEntry routine called IoCreateDevice() for the virtual USB bus, but Windows 11’s new USB stack (introduced in insider builds and backported to 22H2) required a callback that the legacy driver didn’t implement. The bus initialized, but the PnP manager marked it as "failed to start." mastercam+x72022+virtual+usb+bus+error+39+fixed
If the standard methods fail, consider these alternatives commonly used by the Mastercam community:
Here are the proven methods to fix the Virtual USB Bus Error 39, ordered from most likely to least likely. Method 1: Disable Core Isolation (Memory Integrity) Windows security updates frequently turn on "Core Isolation"
This is the first and most successful method for most users. It focuses on using Windows' built-in tools to remove the driver completely.
If you’ve followed this 2000-word guide and still see the yellow bang, your only recourse is to either downgrade to Windows 10 21H2 (and block updates permanently) or upgrade to Mastercam 2024 (which uses a newer licensing system). However, for 95% of users, the steps above will bring your CNC workstation back to life. Click on Core isolation details
Yes, this is a common workaround, though less of a "fix" and more of a system setting change. When you see the message "Windows cannot verify the digital signature for this file," it's because Windows is blocking the driver. To get around this, you can disable driver signature enforcement by restarting your computer and pressing F8 before Windows loads to access the Advanced Boot Options menu, then select "Disable Driver Signature Enforcement" . However, this is a temporary solution that must be done at every boot.
Check group policies or local antivirus software blocking changes to Core Isolation. If you'd like to dive deeper, let me know: