You don't have the Web Images only option selected. So it is probably the file size of the MP3 that is causing the upload to fail.
There are a number of PHP Settings that can effect the maximum file size you will be able to upload.
see this page for details:
for the download problem:
1) Remove the form that is around the repeat region, and add a form around the download button
2) change the download button element from type="button"
<input type="button" id="download" value="Download" name="Download" />
<input type="submit" id="download" value="Download" name="Download" />
3) Add a hidden element next to the download button and bind it's value to the file name column from the recordset.
4) In the download behavior, bind the file settings to the hidden element.