Outlook 2010 is having some severe problems with Ajax based functions. Being a reported error with Microsoft, there is still no fix available, but a workaround.
The impacted product cannot be started inside Outlook, but needs to be launched as a separate IE window.
You need to copy the ostarter.html into the root folder of the products server-side installation and adapt the sitemap as following:
Per default, the sitemap is not having separate entries for WebClient and Outlook-Client, so you need to replace the existing SubArea (ID: nav_GroupCalendar) with these two new entries: