internal server error when try to save a form with more than 6 elements

J3.9.3 CF6.0.22 the system is working perfect on localhost.
When i go to server (php 7) the form is giving an internal server error in administrator when i am trying to save any form that have more than 6 elements!!!

Any more information? What happens if you create a new form and add 7 random things to it and try to save it?

Sorry, my mistake.
All forms have the same behaviour.
Even if i create a total new form. The first few elements saved ok, but after a while (after adding a text area or maybe something else, not always after the sixth element, sometimes after seventh element etc) the saving form button gives server internal error and the quick save button keeps loading eternally.
​
my local php.ini file is as follows
​

allow_url_fopen = On
allow_url_include = Off
asp_tags = Off
display_errors = On
enable_dl = On
file_uploads = On
max_execution_time = 300
max_input_time = 300
max_input_vars = 10000000
memory_limit = 128M
post_max_size = 8M
session.gc_maxlifetime = 1440
session.save_path = "/tmp"
upload_max_filesize = 25M
zlib.output_compression = On
suhosin.get.max_vars = 6000000
suhosin.request.max_vars = 1000000

Any console errors?

No i dont have something to add from web console.
The weird think is the following scenario.
​
Total new form.
6 text fields (OK)
add 1 more text field and one dropdown (total 8 elements) (OK)
​
The same new form
6 text fields (OK)
Adding a button element (7th element) (PROBLEM)

As in the javascript console.

Forget my ignorance but where do i find this console?
Can ypu please advice me?

Press F12. And then ask your host if mod_security is showing any hits blocking your saving.

That on, rings my bell!!!
I have totally disable mod_security and everything is working as it should be. No internal server erros at all