Hi!

I´m trying to optimize my site but I keep getting warnings about the 404 header.. ?

Check the Troubleshooting tab:

www.reactionengine.com/analyse?uri=http:...lekonom&no_se=on


How can I fix that?

It looks to me like there are certain ways to create invalid URLs that still result in 200 OK:

www.mittyrke.se/utbildningsinfo/utbildni...%20m.html342423.html

Ideally, there would be some validation of the URL to ensure it matched valid content before returning the response. I couldn't tell you if it was a Joomla issue or a module one, though.