We recently had a case raised regarding Free Busy issues cross organisations in Exchange 2010 , the 2 organisations couldn’t see each other’s Free/Busy info when looking via Scheduling Assistant.
We spotted the below error in the event log, whenever the free busy lookup occurred we got the below:
“Process Microsoft.Exchange.InfoWorker.Common.Delayed`1[System.String]: <Test@Test.com>SMTP:Test@Test.com failed. Exception returned is Microsoft.Exchange.InfoWorker.Common.Availability.AutoDiscoverFailedException: Autodiscover failed for e-mail address <Test@Test.com>SMTP:Test@Test.com with exception System.Web.Services.Protocols.SoapHeaderException: An error occurred when processing the security tokens in the message.”
This was fixed by running the following command on both customer sites “Get-Federationtrust | Set-Federationtrust –Refreshmetadata”
Straight after running this the free busy issue went away J