05 Freestyle AWD Malfunction

I'm getting a AWD malfuntion message on my Freestyle and its running on front wheel drive now. I just put new tires on, but in the process had to replace the rear hub on the driver side about two weeks ago. It was all good until yesterday I started getting that message. Could it be that one side has a new hub and the other is old? The other side does seem tight with no noise..