- Under the heading "Preparing form data to POST", on the line:
var queryString = '?ArtistName=' + escape(artistName) + '&SongName=' +
The value of "queryString" variable should not start with a question mark.
- Under the heading "POSTing the data", on the line of code:
eval(strResultFunc + '(xmlHttpReq.responseText;);')
There's one semi-colon too many. The one after "xmlHttpReq.responseText" should be removed.