The AuthAnvil Windows Credential Provider will not allow override group members to log on, rejecting them with a "Invalid AuthAnvil Passcode" error. The event log, however, logs a message that the override group member successfully logged on.
The issue is caused by the way that the AuthAnvil Credential Provider 126.96.36.199 handles login attempts with blank passwords.
This bug is fixed in the AuthAnvil Credential Provider 188.8.131.52 and later. You can download and install it from the Customer Portal.
AuthAnvil Credential Provider 184.108.40.206