Make sure that you are following the latest instructions (the latest version of the “YubiKey OS X Login Guide” is on our Documentation page). The most common error that occurs is selecting Require user input (button press) when programming the Challenge-Response. Reprogram your YubiKey without this option selected and you should resolve the issue.
Using the Windows Login Tool
The most common issue is when the option to Require user input (button press) is selected during programming of the YubiKey. Requiring a user input will cause the YubiKey to fail. This is a limitation within Windows, not with the YubiKey. Reprogram your YubiKey without this option selected and you should resolve the issue.
The Windows Login tool works only with Local Accounts (such as “John” or “Sue”). It does not work with a cloud account (such as, email@example.com) or a domain account (such as YOURCOMPANY\John).
Requesting a replacement due to the OpenPGP Vulnerability
When requesting a replacement for a YubiKey NEO, in response to the OpenPGP vulnerability, make sure you provide the order number and serial number for all YubiKey NEO and YubiKey NEO-n devices you want replaced. If you purchased the devices from another source, contact them directly to request replacements.