ModX not responding when accessing to resources

I have ModX Evolution 1.0.2 with over 450 resources/pages.
When acceding to some resources ModX stops working; meaning that appears "working" on the top right of the page and nothing loads.
I tried to clear up the cache, the locks and disconnect & connect again. But still, the same problem.

On those resources I have html, css and some javascript.
Any idea?

Thanks in advance!!

That usually means that mod_security is messing with you. http://wiki.modxcms.com/index.php/What_is_mod_security_and_how_does_it_affect_me