Hello,
My Battle.Net account lists the Knights of the Frozen Throne Adventure as “In my library”. I don’t believe I played the game back when the expansion was current.
When I navigate to “Modes > Solo Adventures > The Frozen Throne” I see there is a “3” notification pip next to Icecrown. After I choose that adventure, I am unable to select the Prologue or any other wing.
The issue did not occur for any other adventure.