Funny I saw your post because I am working on this exact same format conversion as we speak. But NO, I do not have this problem. I can drag and drop fine. Did you try a work around by importing to Premiere first then exporting back to AME?? Did you try to “add” from the file menu instead of drag and drop??
But just to mention, I have the MainConcept Codec Pack for Premiere installed along with the Raylight Decoders.