Ok. The system info already notify for the 1.2.1 and I am already make the update. I will check now these permissions and in minutes I will return. Thanks!
Here is the log:
[2015-10-26 12:53:46] mautic.WARNING: PHP Warning: Cannot modify header information - headers already sent by (output started at /home/maricatenis/public_html/federer/app/bootstrap.php.cache:1441) - in file /home/maricatenis/public_html/federer/app/bundles/CoreBundle/Helper/CookieHelper.php - at line 61 [] []
[2015-10-26 12:53:46] mautic.WARNING: PHP Warning: Cannot modify header information - headers already sent by (output started at /home/maricatenis/public_html/federer/app/bootstrap.php.cache:1441) - in file /home/maricatenis/public_html/federer/app/bundles/CoreBundle/Helper/CookieHelper.php - at line 61 [] []
[2015-10-26 12:53:46] mautic.WARNING: PHP Warning: Cannot modify header information - headers already sent by (output started at /home/maricatenis/public_html/federer/app/bootstrap.php.cache:1441) - in file /home/maricatenis/public_html/federer/app/bundles/CoreBundle/Helper/CookieHelper.php - at line 61 [] []
[2015-10-26 12:53:46] mautic.WARNING: PHP Warning: Cannot modify header information - headers already sent by (output started at /home/maricatenis/public_html/federer/app/bootstrap.php.cache:1441) - in file /home/maricatenis/public_html/federer/app/bundles/CoreBundle/Helper/CookieHelper.php - at line 61 [] []
[2015-10-26 12:53:46] mautic.CRITICAL: Uncaught PHP Exception LogicException: “The controller must return a response (null given). Did you forget to add a return statement somewhere in your controller?” at /home/maricatenis/public_html/federer/app/bootstrap.php.cache line 3063 {“exception”:"[object] (LogicException(code: 0): The controller must return a response (null given). Did you forget to add a return statement somewhere in your controller? at /home/maricatenis/public_html/federer/app/bootstrap.php.cache:3063)"} []
Could you try to rebuild cache? Remove app/cache directory and refresh Mautic. It will be created again.
Yes. I did that. Deleted the cache dir and refresh Mautic. I am waiting for the recreation of the dir again.
How long do you have to wait? It should be done in 2 seconds. If the cache is not created, there is still some permission problem.
Permission is not the problem: 
I don’t know why wait for recreate. But now the dir is there again. What file should I look?
The latest update of Mautic doesn’t solve this misterious problem. And I don’t know where Can be this mautic log for investigating the causes of this mystery.
Well, Its impossible to use Mautic with configuration screen not saving the changes.
And, seems that is impossible to identify the problem without logs alerts.
There are not to do then. I will look for other email system… 
No. I think that I don’t have access to change this feature. Where May I do that on who/cpanel?
Create a .htaccess file in the server root folder and add
SecFilterEngine Off
SecFilterScanPOST Off
Create a .htaccess file in the server root folder and add
SecFilterEngine Off
SecFilterScanPOST Off
Delete this commands after changes.
@tiagorodrigues you are the MAN!
Problem solved!
I have a question: You said to delete these commands when I make the changes. But, if I delete, the problem wont came back?
probably will be back, but now go to your cache folder, clear it. Its mautic/app/cache/
delete everything.
remove the configurations inside .htaccess and check if the problem persists. It’ll probably be fixed soon. It’s most common to happens with shared hosts. If it comes back after you remove, you’ll know what to do while an update doesn’t come to fix. =D
Yes. The problem back.
My server is dedicated. But now I know what to do to fix temporary this issue. Thanks @tiagorodrigues
Hi!
I had the same issues. After checking every suggestion twice I wrote to my webost asking if they use ConfigServer Firewall (mentioned by manageit)
It turned out they did have this Firewall enabled - especially they do this for new accounts.
After my email my admins turned off this firewall and the issue disappeard.
THANK YOU VERY MUCH.
Hello , I have the same error but with different log , see log below;
[2016-01-27 11:43:27] mautic.ERROR: Uncaught PHP Exception SymfonyComponentHttpKernelExceptionNotFoundHttpException: “Requested URL not found: /mautic/s/config” at /home2/aproxima/public_html/mautic/app/bundles/CoreBundle/Controller/CommonController.php line 352
Tks,
Adriano Terres - From Brazil
Nevermind, I found that Wordfence for Wordpress that is running in the same domain was blocking the request.
@alfonso
Hello Friend. Only I decided after I migrated for ubuntu server on DigitalOcean with Bitnami
I’m having this problem but no mod_security installed and no configserver, therefore no clue of what is blocking the connection. Got the 403 but I don’t know how to solve it. I’m running on The Perfect Server Ubuntu 16.04 ( ISPConfig 3.1) and Mautic 2.0