Avidemux+cannot+use+that+file+as+audio+track Exclusive

You are trying to load a MP3 file into a project where Audio Output is set to "AAC" . Avidemux tries to copy the MP3 as AAC, which is impossible. Alternatively, you load a FLAC file when Audio Output is set to "Copy" while outputting to an MP4 container (which doesn’t support FLAC).

In Avidemux:

The most common culprit?