Spark gives invalid username and password - same time of day

A few times a week, between the hours of 2 and 5 pm, my Spark users lose their connection to spark and cannot log back in. They get an invalid username and password error. I am on the helpdesk, but have been told by my server team that the “openfire” service is the one they have to restart to get users to be able to log back in again. We log in with our AD credentials, and unfortunately, I don’t know much more about the environment. We’re on Microsoft Server 2003, as far as I know.

Basically, my server team has no fix, and my callers are getting frustrated. I thought maybe if you had some tips, I could pass them on to our server guys. They told me - and I mean literally - that when I get a Spark expert in here, I can have the problem fixed. In the meantime, this is making support terrible.

Can anyone help?