403 Forbidden / Wrong including show_news.php!

Hello!

First of all:

Thanks to the CuteNews Team for this great product!  ".handle_img_tag($matches[1].$matches[3], false)."

I try to use CuteNews 1.5.3 for my site, BUT $matches[1] (NOT always) I get the following error:

$matches[1]
I included CuteNews with IFRAME:

<iframe src="cn/show_news.php" scrolling="no" width="100%" height="2000" frameborder="0"></iframe>

I have no idea, whats wrong OR why this error comes sporadic?  ".handle_img_tag($matches[1].$matches[3], false)."

Thanks for your help!

Greetings
thrashy