Sorry for your issue. If Jim's advice did not work, open the files on a previous version of Premiere Pro or AME and transcode the footage. Import that footage into the current version of Premiere Pro. Does that work?
Let us know.
This is happening across all of our lab machines and is extremely frustrating as it is end of term and students are frantically trying to complete their assignments. Clips from same camera, same day. Stock footage that is all same codec. Seemingly random as to which clips Premiere chooses to like on any given day. Clearing and rebuilding cache doesn't work consistently. And to tell everyone to transcode their footage defeats the purpose of a workflow that was, until the latest version, working fine!
Has this bug been identified and a fix in the works?