Issue: Duo is not allowing access to a service. The error message is "Access Denied. The username you have entered cannot authenticate with Duo Security. Please contact your system administrator."
Environment: Using a browser, a person having logged into a service using one Falcon Account username is trying to log into another service with a different Falcon Account username. For example, a person logged in with w2600000 is now trying to log in with s2600000. This could happen with a usernames starting with W, S, E, or A (W number, S number, E number, A number).
Resolution: Duo thinks that since these are two different usernames, they are associated with two different people. Duo won't let that happen. Close your browser and log into your desired applications again using one username.