This error code is usually linked to slow/unreliable internet connection. (If you are seeing this when uploading Trackouts only, this would explain why, as trackouts are much larger files than mp3/wavs)
To test your internet connection, run a speed test (if you Google "internet speed test" you can do this in a couple of minutes), and also try downloading/uploading to other platforms to see if everything is ok with your connection.
There's no set number that you need to be above to successfully upload, however you want your upload speed to be at least 10mbps. If you're around 5mbps or lower you will encounter trouble uploading most files as this is too slow.
If you believe your internet connection is fine, please contact support so we can look further into this for you.