Hi @VRayguide,
Can you please share your site url and admin credentials here to check this out on your site.
You can mark your reply as private while sharing the credentials .
Hi @javierbaez,
Please try disabling the third party plugins by renaming the plugin folder names via ftp .
refer :
http://www.wpbeginner.com/plugins/how-to-deactivate-all-plugins-when-not-able-to-access-wp-admin/
and check the siet .
Also check your php configuration .
visit this link for that : your-site.com/wp-admin/index.php?page=wplms-system .
This is our test site configuration .Contact your webhost to have this configuration on your host .
WP Memory Limit: 128 MB
WP Max Upload Size: 64 MB
PHP Post Max Size: 64 MB
PHP Time Limit: 300
PHP Max Input Vars: 1000