If your account is hosted on the Exchange server and the Free/Busy information couldn't be retrieved in Outlook 2007/2010/2013. The free/busy information for other users is displayed as slash marks (/). Note: Free/Busy information missing can be easily confused with Outside of working hours. If you see Free/Busy displayed in light-grey blocks, check your working Hours in Outlook.
There can be several possible causes for that.
- Autodiscover record is missing or set up incorrectly.
You need to make sure that the AutoDiscovery CNAME record has been created for your domain. Outlook 2007/2010/2013 discovers the Availability Service URL using the AutoDiscovery feature in the Exchange environment.
Read the Knowledge Base article on What Is An Autodiscover Record And Why Do I Need It? for more information.
- Default Permissions for Calendar are missing.
Check the Default Calendar permissions for the mailbox you would like to view Free/Busy information for: right-click on a Calendar > Properties > Permissions. The permissions should be set to Free/Busy time to be displayed.
- Calendar is corrupt. Try to start Outlook with cleanfreebusy switch. Start > Run > type outlook.exe /cleanfreebusy