In that case accept my apology for stating that, obviously that's just a general opinion of mine about them because there are always problems with this or that section each day.
From what I can conclude, their requests for validating the existence of the Tweet is being denied by Twitter itself and that's why AMF reports the usual known error because AMF can't "see" the Tweet. Not surprised about this scenario at all. I guess they should redesign the RT/FAV section from scratch.
I believe I'm allowed to suggest YouLikeHits as an alternative, a friend of mine told me about that website and it helped me a bit. It could serve you well if you offer smaller quantities of retweets. There are people on Seoclerks for an example which offer 3,000 RT for $1, 3-4 links split, but who would've known that they create all the retweets within 2-3 minutes, I received 680 on one tweet within seconds. Logically, Twitter couldn't handle and register all the signals added towards the URL written in the Tweet, so that was really a bad experience. Use those sellers only if you must.
There's also one guy on Fiverr who has 838 positive reviews on his "10100 Twitter RETWEETS or Favorites to your post" gig, 5 links split max, so give it a shot if you really need to. I have no idea what's his speed of work though, so be careful.
Good luck