We run Exchange 2010 mailbox servers with users on Outlook 2010.  User A goes to calendar permissions and adds User B with contributor permissions.  User B opens the other user's (user A) calendar and can see it in the calendar view.  So far so good, but now we run into trouble when User B tries to create calendar items in User A's calendar.  Even though we explicitely set User B with create items permissions, the user can't actually add or create anything.  They can see free/busy info which is good, but the create items isn't working.  Is this a known issue or perhaps just the way Outlook misleadingly gives permission options which don't work the way you would intuitively think?  

What we want to accomplish is to allow User B to add calendar items to User A's calendar without seeing existing items in the calendar (aside from free/busy info).  

What am I doing wrong?

Same here - If you mean the contributor permission doesn't provide the "New Appointment" option in the shared calendar.

I tried to grant some different permissions, at least you need to have Author or Publishing Author permission to have the "New Appointment" enabled. With lower permission, it's greyed out. It seems to be by design.

-Jeff