sometimes browser canot use session

[eluser]minhbu[/eluser]
i don`t know why some browser cannot use session
i use
i set value $this->session->set_userdata("demo",1);
i get value $value_session=$this->session->userdata("demo");
sometimes i get value is empty
help me

[eluser]TheFuzzy0ne[/eluser]
Can you be more specific? Which browsers are you referring to?

I've found that sometimes, certain characters, such as a slash, can break a cookie.