Best answer by Navid
To be on the safe side, make sure your file is exported in .wav or .mp3 and encoded in 44.1kHz and 16bit.
Try uploading through an ethernet connection instead of a wifi network, that usually works best.
Lastly, for the encoding process to take place in the best possible way, we recommend you leaving all the fields empty except for the title, until the track was fully uploaded and has entered processing. (Orange half of the upload bar)
Hope this was helpful!