Drupal cannot generate the derived image ANYMORE? OK, My situation is really complicated (or Im stupid).
I start my website http://rlsgame.org with Drupal System (even if Im .NET developer)...
After 3 month, my website start grow up (about 2000 article and 3000 members) But a problem appear !!! I didnt touch anything, It appear just like that !!

When I want submit a Node, I have an issue with Images, I cant see the preview image :



and After submiting the Node, here is the result:



I refresh the page and the nothing, But after i press CTR+F5, the article is fine:



you can check the page here: http://rlsgame.org/PC/Games/ArmA-III
All is fine...

But the big problem is that Drupal System cannot generate the derived image of User Picture !!
Even if I press CTR+F5 like before, the problem is still here, look an exemple of a profile page:


Link: http://rlsgame.org/users/gamer

The old users profile is fine, because the picture is generated before the problem, exemple:


Link: http://rlsgame.org/users/mgs

And one more thing it start to appear too, Drupal start Caching comments (not like before this problem), when I post comment, sometimes it apear without Caching, and sometimes I must wait about 10 sec, for exemple, I post a comment and nothing appear, and I navigate to the homepage, and here we go, the msg appears:



I think if I fix the issue, All those problems will disappear ...

Im looking for fixing that 10 days ago, So Just for info:


All files permission Are OK:
sites/default  => 555
sites/default/files  => 755  (and all sub-folders too including styles)
And paths of File system are OK
Drupal is updated to 7.26 (latest version)


And the problem is not from the server (Im working on Shared Server) because I downloaded my website and run it in Local but I see the same problem plus My website work before so the problem is not from the server. 

Ah, one thing, when i check Reports Log, I see a lot of warning, here is an exemple:



Thats all, plz help me to fix that, Im losing traffic....

Thanx for advance.
In your settings.php file add this

$conf['image_allow_insecure_derivatives'] = TRUE;


In the future you should use image_style_url() when using image styles as this will then add in itok parameter for images. Usage: image_style_url doesn&#39;t create images

More info about this: https://drupal.org/drupal-7.21-release-notes