I've tried to do the sample 'Receiving Notifications in a Visualforce Page' of the page http://wiki.developerforce.com/index.php/Getting_Started_with_the_Force.com_Streaming_API

I'm doing everything as it comes in the document but don't get it to work. I'm on the na12 instance. When I try it on Chrome It gives me these errors

POST https://c.na12.visual.force.com/cometd/handshake 401 (Request requires authentication)

I also tried the equivalent sample of the document http://www.salesforce.com/us/developer/docs/api_streaming/api_streaming.pdf (page 11) but It gives me these errors

Uncaught TypeError: Object [object Object] has no method 'reset'
org.cometd.LongPollingTransport.resetcometd_js:2102
resetcometd_js:120
_handshakecometd_js:730
handshakecometd_js:1421
initcometd_js:1409
(anonymous function)StreamingPagePDF:89
d.extend._Deferred.f.resolveWithjquery.min.js:16
d.extend.readyjquery.min.js:16
c.addEventListener.y

I don't know what to do

Thank you in advance

David