Google Adsense Ads is incompatible with documents rendered with the application/xhtml+xml MIME type.
This is the case with the current version of Instiki, which emits XHTML.
The problem is due to the embedded Google javascript that uses document.write() to modify the document.
One solution is to use the html object tag to insert a separate html snippet that has the MIME type set to “text/html”.
An implementation that works with IE6 as well as Firefox is described here