You will see this error when our system is having trouble processing a track, causing it to be stuck as it waits to transcode. 

When this happens, we recommend the following:

• Check the file format and length of your track. We support AIFF, WAVE (WAV), FLAC, ALAC, OGG, MP2, MP3, AAC, AMR, and WMA files. The maximum file size is 5GB.
• Check our Status Blog to make sure that there are not any problems occurring around the transcoding process at this time. 
• Delete the pending track from your SoundCloud profile and re-upload it.