The following happens, and is repeatable for any movie, ONLY when selecting any of the mp4 presets and attempting to include 2 soundtracks (1 works just fine):

15:59:52 3072 Available files:
15:59:52 3072 File "D:Encodefairuseinsoup.session-00.video-stream.0.264" is 518.65 MB (543842978 bytes)
15:59:52 3072 File "D:Encodefairuseinsoup.session-00.audio-00.aac.aac" not found!
15:59:52 3072 -----------------------------------------------------
15:59:52 3072 Preset : H.264/AAC/MP4, Fast
15:59:52 3072 Container : MP4
15:59:52 3072 Video codec: x264
15:59:52 3072 Audio track 1: AAC
15:59:52 3072 Audio track 2: none
15:59:52 3072 -----------------------------------------------------
15:59:52 3072 Will create final file with following command line
15:59:52 3072 "C:Program FilesFairUse Wizard 2mp4box.exe" -nodrop  -fps 23.976024 -add "D:Encodefairuseinsoup.session-00.video-stream.0.264#video" -add "D:Encodefairuseinsoup.session-00.audio-00.aac.aac" -new "D:Encodefairuseinsoup.mp4"
16:01:02 3072 File "D:Encodefairuseinsoup.mp4" not found!
16:01:02 3072 -----------------------------------------------------
16:01:02 3072 _OutputProcess() : Muxing failed (aborting)
16:01:02 3072 _TranscodeProcess() : Muxing failed!