Every now and then I hear complaints about Free/Busy information retrieval issues. There are a lot of reasons for such issues, but the interesting part by these issues is that accessing the shared Calendar is not a problem. Only when users set up a meeting and using the Scheduling Assistant, they suddenly see only the beloved hash marks:
Using OWA the user was able to retrieve Free/Busy information using Scheduling Assistant.
And this happens usual to VIPs like the CEO or CIO. So I started troubleshooting with highest priority and found an easy fix.
An assistant tried to set up a meeting. Once the Scheduling Assistant was used, only hash marks were shown. But accessing the shared folder was working. In OWA the user was able to retrieve information using the Scheduling Assistant.
First thing was to check permissions on the NON_IPM_SUBTREE folder Freebusy Data
Note: If the mailbox has a delegate, you will see here the same permissions as on the Calendar folder.
As there was nothing obvious, I checked the EWS logs on the server, where the target mailbox resides, with my script Get-EWSStats.ps1. But no errors were logged. Even a Fiddler trace showed me that the client retrieved the information, but for some reason the client encountered an issue.
But then I stumbled across a post from fellow MCM and MVP Michel de Rooij, which pushed me into the right direction:
In his post Clearing AutoComplete and other Recipient Caches he explains in details how AutoComplete works and that there are two different caches. One for Outlook and one for OWA.
As in my case it was working for OWA, but not for Outlook, we just deleted the entry for the affected recipient in Outlook and everything started working.
We don’t know what caused the corruption of this entry, but as the fix was an easy one we decided not to spent more time on this.
I know that this solution will not be the fix for all issues, but you should add this to your troubleshooting steps as this is a quick one. Especially when you came from or just performing a migration project.