Can not retrieve free/busy

I'm running Exchange 2000 servers.
I have about 10 users on same exchange server and on same SG and Mailbox
store.

When I schedule a meeting and invite those 10 users as required attendees.
Only 3 users free/busy schedule is displayed and rest of the attendees show
'no info' grid (black stripes on white).

I dont get to see even 2 months of information.

I ran yesterday outlook /cleanfreebusy on all 7users and I could see
free/busy information on all 10 users. However this morning everything came
back to square one, with only 3 users' free/busy information displaying.

Could anyone help me out please.

Thanks,