Website features are protected to be disabled if the PHP system functions (exec,passthru,shell_exec,system,popen,proc_open) are not disabled for the website context.
The value "exec" has NOT been found into the current disable_functions=
dl,apache_note,apache_setenv,pcntl_alarm,pcntl_fork,pcntl_waitpid,pcntl_wait,pcntl_wifexited,pcntl_wifstopped,pcntl_wifsignaled,pcntl_wifcontinued,pcntl_wexitstatus,pcntl_wtermsig,pcntl_wstopsig,pcntl_signal,pcntl_signal_get_handler,pcntl_signal_dispatch,pcntl_get_last_error,pcntl_strerror,pcntl_sigprocmask,pcntl_sigwaitinfo,pcntl_sigtimedwait,pcntl_exec,pcntl_getpriority,pcntl_setpriority,pcntl_async_signals,show_source,virtual,passthru,shell_exec,system,proc_open,popen

You can fix this by changing setup of your PHP ini (changing this in a virtual host with php_admin_value is not effective):
disable_functions="exec,passthru,shell_exec,system,popen,proc_open,..."
but WARNING, this may also break features for:
- cron tasks calling command line tools.
- and for the backup feature running the database dump tool.
- and for the command line antivirus check ran when uploading a file.

If you don't use this 3 feature, change your php.ini, if you need at least one, you can bypass this protection by setting $dolibarr_website_allow_custom_php to 2 in your dolibarr config file.