I'm hoping you can help me, too. I just found out about/signed up with Quantcast today. I installed your plugin, all of which seemed fine, but I keep getting this error message from Quantcast when I go to scan the site:
Quantcast was unable to find a tag on the URL you entered above. Please make sure the tag is placed on all of the pages of your website exactly as it appears above.
I'm using the Mystique theme, btw. Anyway, I tried it with enabling the code to go in the footer, then disabling that and having it in the header, but neither one shows up in the code when I check it in the Editor section...which explains why Quantcast can't do the scan.
The code also doesn't show up when I go to my site and click on "View Page Source."
I saw your note about excluding the Start & End Tag lines, and I did that as well.
And finally I should mention that whenever I changed the settings, I did save them and saw the "Settings Saved" note.
So at this point I'm flummoxed, and any advice you can provide would be much appreciated!