Problem: Your company takes security seriously and do not wish that the anonymous calendar sharing which comes with Exchange 2010 SP1 (which is enabled by default) is used.
Solution: You can disable the calendar sharing option with the below powershell comand, which must be used against every CAS server you are using:
Set-OWAVirtualDirectory -Identity "YourExchangecasServerNameHere\owa (Default Web Site)" –CalendarPublishingEnabled:$false
