Hello,

I am not sure if that is error or typo or what, but the links (non-sef) you write for RSS:
index.php?option=com_content&format=feed&id=98&index_php/moda-omorfia/o-kairos_html?option=com_content&layout=blog&type=rss&view=category

is certainly not valid. It includes 2x ?option=, etc. If this is really the original link that shows in your site, the I think the problem must be in template or some customization or hack you have in place.

I have tested this on a clean Joomla instalaltion with default template and there is works just fine.

Here is a link that works
www.istories.gr/index.php?option=com_con...s&view=frontpage

but this is usually turns into www.istories.gr/rss.html <- which is not working

I have same problem

And what is the non seo format of "www.istories.gr/rss.html" stored in JoomSEF DB?

I will give you an existing one so you can see.

www.istories.gr/anakoinoseis/rss-3.html <- this is the one that it is created

and this is what is stored in DB

index.php?option=com_content&format=feed&id=98&index_php/theatro/o-kairos_html?option=com_content&layout=blog&type=rss&view=category

index.php?format=feed&type=atom stored in db