Are you on a shared webhosting?
The easiest method is to contact helpdesk and ask them to fix your access to session directory, as I doubt you have full access to php settins as a user where you can set the path to session store directory in.user.ini
But if you can at least set the ini variables in php, you can try this approach.
1. create a directory named for example 'sessions' outside of public_html directory
2. give this directory full rw permissions (777)
3. set the session path to this dir in bludit before session starts. I'd hit the /kernel/boot/admin.php file and change the
I can't guarantee that it will work. Even if, consider this as a temporary solution, as It is risky to use in security means.