Calendar Permissions Missing After Migration from Exchange 2003 to 2010

All employees use Outlook 2007.  I have migrated our Exchange environment from Exchange 2003 to Exchange 2010 probably 3 months ago.

One user’s calendar (we will call him Tom)  was not showing Free/Busy information to any other user who had added Tom’s calendar to their Outlook.  In addition Tom mentioned that when he tried to edit his own calendar permissions it was throwing errors.

I added the user’s calendar to my Outlook (which is version 2010) and nothing showed up.  I then setup an email profile for Tom on my computer and logged in and looked at his calendar permissions.  And, there were none.  Not even the default permissions, which was pretty awesome.  So I added in myself, clicked OK and it came up with the error message saying “Unable to Modify Permissions”.  I logged in as Tom through OWA and tried to modify the permissions and the same error occurred.

At this point I did what any good SysAdmin does and break out my Google Fu to see if it can shed any light on this issue, because I have no idea how to get the default permission to show up short of recreating the mailbox and I don’t quite want to go that route yet.  Sure enough after about 10 minutes of digging I came across this article (SysAdmin fail, I didn’t save the right link.  Crap.) that said one way to recreate the default permission was to add someone as a delegate and then remove.

So I added myself as a delegate to Tom’s mailbox, closed out of Outlook, reopened Outlook and removed myself and then verified on Tom’s calendar that the default permission was now present.  I then logged into Outlook as myself and wasn’t able to view his Free/Busy information yet, but I was through OWA.  A few hours later Tom’s Free/Busy calendar information was showing in my Outlook and was for other users as well.