Logon Events Missing

[Elway7]

I have two users that when they log in to the domain there are no security events logged at all, but they computers they log in with do log security events.
I only noticed this b/c when they log in an application is launched that uses a single sign on. For everyone else this works fine except for these two users who are prompted to enter their username, password and domain.
It is almost like they are not getting authenticated to the domain.
Any thoughts?

Thanks