Outlook 2007 : Why i can’t accept an invitation that is in a third-party calendar format?

One of my customer updated that they have an application which uses Outlook Object Model which usually receives the invitation and process it. But when has issues for a specific invitation to a meeting in Microsoft Outlook 2007. This impacts him that he can’t no longer accept the invitation. When we researched regarding the issue, we found it’s not with respect to the code. We found that the invitation is generated and present in a third-party calendar format (ical).

This issue is fixed in the Outlook 2007 post-Service Pack 1 Hotfix Package that was released on January 28, 2008.