Call javascript (jquery) from iframe on parent?

[eluser]Sven Delle[/eluser]
Struggling with fileupload, I'm trying to inject some javascript code into the iframe used for uploading a file.

I can send:

Code:

echo '[removed]alert("SUCCESS FROM IFRAME");[removed]';

to the iframe and have it work, but I can't send:

Code:

echo "[removed]$('#admin_content').html('HOORAY!!!');[removed]";

Now, is that security or something preventing this?