If you received the error like:  Authentication failure:  Invalid username or password"  after you've correctly entered in your NetID and password, you maybe locked out of Duo Security two-step login.  This can happen with any system that requires two-step login.

Example of authentication failure:

Please call 2-9800 or submit a service ticket so that a Duo Administrator can unlock your account. 

Also, ensure that the device in hand is listed as your default device in the Duo Self-Service Portal to prevent being locked out again

Be sure to keep your default device handy when you log into a protected system that requires 2-step login.