Difficulties in executing PHP code using Exec-PHP

Hi, I am intending to generate RSS feed article into my blog. I am using Exec-PHP to execute PHP code into write post-> HTML editor function. I generate PHP code using RSSfeedreader.

When I execute the code, always its said

“The URL you supplied is either not RSS or the site is down at this time. Please check the feed URL or refresh the page.”

I’m trying to generate RSS feed PHP code from 10 site, and when I execute the code (write it in the post), the same text always appear?
I dont believe that 10 sites can be down at the same time.

Can someone help me please

Thank you