The error about no results is letting you know that the query is not returning any results. Have you confirmed that you are logged in with a user that has the purchase in their order history? The user id must be set in the session, and the user must have a record in their order history that points to an item with a value in the mp3_path column.
As for the js error you are getting you should close DW and try deleting the cache file, here are some instructions on how you can do this:
common_installation_issues.pdf
