Exchange 2007 server was getting error eventID 8207:

Error updating public folder with free/busy information on virtual machine SERVERNAME. The error number is 0x80004005.

This is generally caused when you upgraded from 2000/2003 and didn’t put in replicas for the old email groups.
You can find out by opening the powershell and running the following:
Get-PublicFolder -Identity "\NON_IPM_SUBTREE\SCHEDULE+ FREE BUSY" -Recurse | fl name,Replicas

In my case I got

Well I had my Back-End Admins group (the one from exchange 2003) had a Replicas {} listed. The screen shot shows what it *should* look like.

To fix, just copy the FB information to your current public folder database:
Set-PublicFolder -Identity "\NON_IPM_SUBTREE\SCHEDULE+ FREE BUSY\EX:/o=lkj/ou=Back-End Admins" -replicas "EXCHANGESERVER\Second Storage Group\Public Folder Database"

And then, if you’re not a patient person, run outlook via the following:
outlook.exe /cleanfreebusy