there's a ' missing after yourpopup.php:
but this shouldn't give errors in Flash, only in the browser.
I guess the error in Flash is because there are linebreaks in the
string. It has to be all in 1 line, not splitted on 2 or more lines
(yep, it sucks, but that's how it is...)
If it's not that, please post what the output brings up.