This issue may also occur when clicking on Skype items and email voice mails.
STATUS: WORKAROUND For more information on this issue, please go to Outlook hangs when clicking in Conversation History folder.
6] There are also a few command switches that can help you reset, restore or fix certain Outlook functions.
Take a look at this post – Troubleshoot Microsoft Outlook problems, to learn more about this.
7] Use the Microsoft Office Configuration Analyzer Tool.