New to Spark - Customer cannot log in to Spark

Hello, New to Spark and OpenFire. A previous IT loaded the Spark Messenger Service onto the Servers and we have successfully migrated the services to a new Server. However, after about a month of running smoothly, there is an error that the user cannot login. They have verified that the service is running on the Server and that the client is running. However, they get bad username and password. What are we missing? Any help would be greatly appreciated.

Check the logs and post here.
Error Logs:
C:\Users\User\AppData\Roaming\Spark\logs
There is a bunch of files, look through all of them and select events that correlate with the time of your issue.