Using relative reference with '.download'

Does anyone know a way to use a relative reference with the download?
I would be surprised if only absolute references will work but I can’t find a solution.

This code just gives me this error (as expect by the live docs)
Error #2039: Invalid remote URL protocol. The remote URL protocol must be HTTP or HTTPS.

trace(s);//someFile.pdf			
var downloadURL:URLRequest= new URLRequest(s);
var fileName:String=s;
var file:FileReference= new FileReference();
file.download(downloadURL, fileName);

livedoc ref here:
http://help.adobe.com/en_US/AS3LCR/Flash_10.0/flash/net/FileReference.html#download()

Thanks for taking the time to look at my problem.
S.