can't view free/busy schedule with Outlook 2003

I just installed Exchange 2007 into our existing Exchange 2003 organization
and everything is working fine except for free/busy information. I've
replicated the system folders (OAB & Schedule+ Free Busy) to Exchange 2007.

1) 2003 Mailbox users cannot see any 2007 Mailbox users free/busy schedule,
it shows lines through it ands says "No free/busy information could be
retrieved". They can only see 2003 Mailbox users free/busy schedule.

2) 2007 Mailbox users using Outlook 2003 are able to see the free/busy
schedule for 2003 users but not all the information shows up for 2007 Mailbox
users only some of the items are showing up (better than no information).

3) 2007 Mailbox users using Outlook 2007 are able to see the free/busy
schedule for both 2003 & 2007 Mailbox users.

Any ideas?