I was working on proof of concept Outlook add-in for a customer when I ran into series of distressing exceptions trying to access specific recurring appointments from the calendar. There seems to be a great many ways to get a list of appointments for a specific date, but you may find the .Start date of these vary wildly. I went down a path using GetRecurrencePattern().GetOccurrence(DateTime.Now), and I got this exception a LOT:
“You changed one of the recurrences of this item, and this instance no longer exists. Close any open items and try again.”
After doing some more searching, I found that I was going about it all wrong. Now, I will be the first to say that I am not the strongest in the Outlook Object Model. Excel, Word and especially PowerPoint are by bread and butter. But sometimes, Outlook can be just downright confusing. 
In the end, this is what I came up with to get a list of all the appointments on a given date in a specific users calendar that you select from the Address list:
Outlook.Recipient LobjRecipient = null;
// crete a select names dialog
Outlook.SelectNamesDialog LobjSnd = MobjOutlook.Session.GetSelectNamesDialog();
// limit to the TO box
LobjSnd.NumberOfRecipientSelectors = Outlook.OlRecipientSelectors.olShowTo;
LobjSnd.AllowMultipleSelection = false; // there can be only one
LobjSnd.Display(); // display it
// do we have resolved names
if (!LobjSnd.Recipients.ResolveAll())
{
LobjRecipient = null; // NO
return; // exit out
}
else
{
LobjRecipient = LobjSnd.Recipients[1]; // yes
}
LobjSnd = null;
// open the shares Calendar folder
Outlook.MAPIFolder LobjFolder = MobjOutlook.ActiveExplorer().Session.GetSharedDefaultFolder(
LobjRecipient, Outlook.OlDefaultFolders.olFolderCalendar)
as Outlook.MAPIFolder;
// get all the items
Outlook.Items LobjItems = LobjFolder.Items;
LobjItems.Sort("[Start]"); // sort the items by start date
LobjItems.IncludeRecurrences = true; // be sure to include recurrences
string LstrDay = DateTime.Now.ToShortDateString(); // today
// set the find string to today 0:00 to 23:59:59
string LstrFind = "[Start] <= \"" + LstrDay + " 11:59 PM\"" +
" AND [End] > \"" + LstrDay + " 12:00 AM\"";
// find the first appointment for the day
Outlook.AppointmentItem LobjAppt = LobjItems.Find(LstrFind);
while (LobjAppt != null)
{
// ...do your thing here...
// get the next item
LobjAppt = LobjItems.FindNext();
}