When a card prompts you to "discard an ally" can you discard an objective-ally? (I am assuming you are playing a scenario where an objective ally can be discarded without instantly losing the game).
I was playing The Road to Isengard last night, where the first stage allows you to "bid" for up to four Ent of Fanghorn objective-allies. I won all four, but if I hadn't I would have had to remove the rest from the game. Much later in the game I was forced to discard an ally, so I discarded one of these ents (the least valuable card in the game to me at that time), and placed it in the discard pile. I lost two more of these ents a little later, and again placed them in the discard pile. A while later I had to reshuffle the encounter deck, and a bit later drew an Ent of Fanghorn, which I placed in the staging area and immediately started "bidding" for it (thanks to a lot of readying and Eowyn I won it back the same turn I drew it!).
So did I play this correctly?
(I really hope so, as it took about 2.5 hours to play, and at one point I dumped 21 points of damage on Saruman in one go, so I could concentrate on questing to win the game, which I did! Though Pippin died, so I will have to replay, anyway.)