Why do I get Unsupported media file in Subtitle Workshop for a MP4 file?

Forum: Subtitling
Topic: Why do I get Unsupported media file in Subtitle Workshop for a MP4 file?
Poster: Fredrik Pettersson

I choose Video, Open... and browse to the MP4 file to open it in Subtitle Workshop. But I get an error message upon doing that:

Error. Unsupported media file (filename.mp4).

I have the latest version of Subtitle Workshop installed.