Insert HTML Snippets breaking WordPress Install

I get a major error when I activate or install this script on my site

The plugin generated 323 characters of unexpected output during activation. If you notice “headers already sent” messages, problems with syndication feeds or other issues, try deactivating or removing this plugin.

It makes the ‘feed’ stop working on the site and messes up the headers.

I use this great plugin on several sites and I used it on this site, after an upgrade the broken feed and messed up headers started.

I tried to uninstall the plugin and even that makes errors

New install the same thing

So is there a major bug now in this script

I also had this script recently crash the entire server on another site, the reason, the script created a heavy load on the feed in an endless loop, as soon as I would turn on the script, it would hit the /feed and never stop, load would quickly go from 1 or 2 up to 100 or 200 in a few minutes crashing the entire server.

So is this script now useless?