Can't Import Videos Anymore

Ive recently tried to import an animated video onto the iStopmotion timeline for rotoscoping purposes, but for some reason, it doesn’t work now and says that they are unsupported files. Ive tried MOV, MP4, MPEG and even GIF formats but they have the same result. It has imported these file types before with no problems. Is it to do with a new update? Has anyone else had this issue? If so, how did you resolve it?