upload header logo gives error

[Kiona]

Hi, I'm a newbe, and I'm trying to upload a .jpg image in the 'admin' area (back-end of prestashop). But i get an error by loading the site:
SmartyException in smarty_internal_templatebase.php line 129: Unable to load template file '/index.tpl'

1. in smarty_internal_templatebase.php line 129
2. at Smarty_Internal_TemplateBase->fetch('/index.tpl', null, 'layouts/layout-full-width.tpl', null, false, true, false) in SmartyCustom.php line 110
3. at SmartyCustomCore->fetch('/index.tpl', null, 'layouts/layout-full-width.tpl') in FrontController.php line 671
4. at FrontControllerCore->smartyOutputContent('/index.tpl') in FrontController.php line 655
5. at FrontControllerCore->display() in Controller.php line 225
6. at ControllerCore->run() in Dispatcher.php line 379
7. at DispatcherCore->dispatch() in index.php line 28
    

I looked in the img folder on the server and see that the name of the image is getting a number and the Permissions are 644, So I changed it to 755, as like the original logo.

But that also didn't fix it. I'm using prestashop 1.7.2.4 with the default theme 'classic'. The website is: https://valkenet.com/7/index.php

The index.tpl is in the folder: public_html/7/themes/classic/templates, with 0755 Permissions.

Hope someone knows what I did wrong.

Edited December 19, 2017 by Kiona (see edit history)

[NemoPS]

Sounds like a mod security issue, can you see if it's active on the server, and eventually disable it?

[Kiona]

Hi NemoPS,

Thanks for your answer. I don't have a mod secutity plugin in cPanel.
I put it in in to the .htaccess file. But that doesn't make any difference.

What i do see now is that the shop is working in the browser Safari.
Firefox and Chrome is given the error message. I emptied the cache, cleaned the browsers restarted the browser, nothing helped.

Any other idea?

 

Thanks already,

[NemoPS]

No idea right now, the odd thing is that it tries to load a front template when uplading, since you are in the BO