Below is what I sent to Jack as he sent me the mp3 that worked on my machine after I corrected it in audacity. MP3 and wav files are the only ones i have tried and I know they both work. Wav seem to work better with the scrubbing, but the choice is yours
Jack,
Using audacity I converted the mp3 to 44100, 16 bit (the one you sent was 32 bit) 128kbs, constant, and stereo stereo and the used that file into the sequence. I saved the sequence and brought it into the scheduler with no problem.
That mp3 is all I changed and then resaved the sequence. I have reattached the mp3, the msq was not changed Try it using this mp3.
I am using build 11338.1054
Hope this works for you.
Merry Christmas
Mike