What happened to my Inbox in iCal for shared event notifications?

My husband and I share a calendar. Until recently, when he added an event, I would hear a "ding" and see a number flag pop up on the iCal icon in my Dock on my MBP. When I would open the iCal app, I would see in the upper left corner an Inbox. When I would click on the inbox, it would give me the details of the newly added event and the date on which it was scheduled. When I would click "OK," the number flag would disappear from the Dock. This has worked great for years.

But, as of about a week ago, there is no longer an Inbox on my iCal page on my MBP, even though I'm still seeing the number flag in the Dock. The only way I can find out the what/when info for the new event is to go to my iPhone, click on iCal, go to the Inbox (which still appears on my phone, thank goodness), and find out what the new event is and when it's scheduled. When I click "OK," the number flag disappears from the iCal icon both on my phone and in my Dock on my MBP.

Is anyone else missing an Inbox? Anyone have a solution?