Cannot modify header information aioseop.class.php:4545 Installation / Upgrading - All in One SEO Pack Forum

I'm trying to enable All in One SEO Pack, but I'm getting this error from the feedburner plugin:

Warning: Cannot modify header information – headers already sent by (output started at /home/public_html/blog/wp-content/plugins/all-in-one-seo-pack/aioseop.class.php:4545) in /home/public_html/blog/wp-content/plugins/FeedBurner_FeedSmith_Plugin.php on line 113

Warning: Cannot modify header information – headers already sent by (output started at /home/public_html/blog/wp-content/plugins/all-in-one-seo-pack/aioseop.class.php:4545) in /home/public_html/blog/wp-content/plugins/FeedBurner_FeedSmith_Plugin.php on line 114

Now… I thought this might be that plugin error, so I disabled it and tried again.

Feedburner says this:
The URL does not appear to reference a valid XML file. We encountered the following problem: Error on line 4: The markup in the document following the root element must be well-formed.

And Firefox shows:
Warning: Cannot modify header information – headers already sent by (output started at /home/public_html/blog/wp-content/plugins/all-in-one-seo-pack/aioseop.class.php:4545) in /home/public_html/blog/wp-includes/feed-rss2.php on line 8

Using: Versión 1.6.12.2
WordPress 3.0.1.

I deactivated all the plugins and activated them, AiO was the last one, unfortunately, the error showed again.

Don't know what is wrong, both sites I upgraded are the same.

Could it be a VPS issue with software?
I'm under Linux, Apache v2.2.16, PHP 5.2.14, MySQL 5.1.48

Thanks