Fix SCARD_W_UNRESPONSIVE_CARD (0x80100066) Smart Card Error

Quick Answer

Clean the card contacts with a dry cloth, restart the smart card service, and reinstall the reader driver. If that doesn't work, the card itself is likely dead.

Why This Happens

Error 0x80100066 pops up when Windows sends a reset command to the card but gets nothing back. The operating system sees the reader, the reader sees the card, but the card won't acknowledge the reset. I've seen this most often with government PIV/CAC cards and Yubikeys after someone unplugs the reader mid-transaction or after a bad USB hub brownout.

The culprit here is almost always one of three things: dirty contacts on the card or reader, a corrupted driver stack for the reader, or a card that's physically damaged. Rarely, it's a dead smart card service — but that's an easy check.

Fix Steps

Clean the card and reader contacts. Take a lint-free cloth or a coffee filter (paper towels leave fibers) and gently wipe the gold chip on the card. Also blow compressed air into the reader slot or wipe the reader contacts with a dry Q-tip. This fixes about 40% of cases.
Restart the smart card service. Open an admin Command Prompt and run:
```
net stop SCardSvr && net start SCardSvr
```
Then plug the card back in and try again.
Reinstall the reader driver. Go to Device Manager, expand "Smart card readers", right-click your reader (might show as "Broadcom USH" or "OMNIKEY" or "Identiv"), and select "Uninstall device". Check "Delete the driver software for this device" if offered. Reboot — Windows will reinstall the driver on boot.
Use the Microsoft Generic driver instead. If your reader's custom driver is flaky, override it. In Device Manager, right-click the reader, select "Update driver" > "Browse my computer for drivers" > "Let me pick from a list..." > select "Microsoft Usbccid Smartcard Driver (WUDF)". This generic driver is rock-solid.
Test with a different card. Borrow a coworker's card. If theirs works, your card is dead. If theirs also fails, your reader or driver is the problem.

Alternative Fixes If the Main Ones Fail

Check USB power delivery. Plug the reader into a powered USB hub or directly into the motherboard USB port. Some readers need 500mA and a front-panel USB port can't deliver that.
Disable selective suspend for USB. Open Power Options, click "Change plan settings" > "Change advanced power settings". Expand "USB settings" > "USB selective suspend setting" and set to "Disabled".
Remove and re-add the card in the registry. Open Regedit, navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Cryptography\Calais\Readers. Delete any subkeys with the reader name. Reboot and reinsert the card.
Update the reader firmware. Visit the reader manufacturer's website (e.g., Identiv, HID Global, Yubico) and check for firmware updates. This is rare but I've seen it fix odd timing issues.

Prevention

Don't yank the card out. Always use the "Safely Remove Hardware" option or at least wait for the activity light to stop blinking.
Keep the reader clean. Dust and coffee spills kill these things. Give the reader a blast of compressed air every month if it's in a high-traffic area.
Update reader drivers once a year. Check the manufacturer's site. Don't rely on Windows Update for these — it's lazy and often delivers generic versions that miss features.

If you've gone through all that and the error still shows up, the reader hardware is probably toast. They're cheap — swap it out and move on with your day.