How can Outlook 2007 open a Lotus Notes Calendar invite?

We have Outlook 2007 and have received a Calendar Invite from a client. The attached Calendar Invite has an ics extension. Problem is, when double click to open it, all we get is this error message: Invalid Internet Calendar

I sent the attached home where I have Outlook 2003 and it opens as a regular Calendar Invite where you can Accept, Decline, Tentative etc…

We need to be able to open this type of invite in Outlook 2007 and 2010 as that is what we use. Can you please tell me how to fix this issue.

Thank you so much!

Please note: It doesn’t seem to matter what the OS is, it’s the Outlook version.