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If a recent Windows 11 update stopped your ProLine or MicroLine camera, CFW/CenterLine filter wheel or Atlas focuser from being detected, the Windows Driver Policy may be blocking the FLI USB driver (fliusb64.sys). Hansjörg Wälchli of upsky.ch got his ProLine 16803 working again by turning that policy off, following Microsoft's own instructions. It's an interim workaround until our signed driver is ready.

What happened. Windows 11 updates from April 2026 added a Windows Driver Policy. On some PCs it stops the older FLI USB driver, fliusb64.sys, from loading. This affects ProLine and MicroLine CCD cameras, CFW and CenterLine filter wheels (including a filter wheel used alongside a Kepler), and the Atlas focuser. Kepler cameras aren't affected. Their software installs normally on Windows 11.

What Hansjörg did. Hansjörg found that his ProLine 16803 worked again after he turned off the Windows Driver Policy, as Microsoft explains here: https://support.microsoft.com/en-us/windows/hardware/drivers/the-windows-driver-policy

Microsoft's page explains how to check whether the policy is what's blocking a driver and how to turn it off. The steps depend on which Windows updates you have installed, so follow Microsoft's page directly. These are Microsoft's instructions, not FLI's.

Before you try it.

• Check the cause first. This only helps if the Windows Driver Policy is what's blocking fliusb64.sys. Use Microsoft's page to confirm that before changing anything.
• Talk to your IT department. You need administrator rights, and Microsoft warns that turning off the policy lowers your PC's security. Managed or Enterprise PCs may have their own IT policies that keep blocking the driver anyway.
• Turn Secure Boot back on. If your PC needs Microsoft's older steps, the ones that involve driver signature enforcement (DSE), re-enable Secure Boot afterwards as Microsoft directs.
• Results vary. A customer has reported that this resolved the driver block on their ProLine camera under Windows 11. Results may vary by Windows version and by IT-managed security settings, so please check with your IT department first. If it doesn't work on your system, contact our support team.

A signed driver is in preparation. We're preparing a signed FLI USB driver. We don't have a release date yet. When it's available, install it and turn the Windows Driver Policy back on.

Thank you, Hansjörg, for sharing what you found. Questions? Contact our support team.