Ack, the dreaded RED X. When you get an error processing, we send you an email notification with more specifics about why your file is bad. Reminder: currently you can only upload an MP2 to PRX.
An error processing either means you are uploading the wrong type of file or your original file does not have the correct specifications. You should be starting with a 16 bit integer WAV or AIFF file and converting that file to an MP2 using the Hindenburg PRX Encoder.
Once you have a better file, remove your old file and upload your new one.
If you continue to have trouble, just let us know.