DEDECMS SEESION有关问题

DEDECMS SEESION问题
我是DEDE5.7的PHP5.4的，刚开始空白，说是 @session_register不兼容5.4的，我按照网上说的注视，提示说，登陆成功，但是又回到登陆见面出来这俩个错误

Warning: Unknown: The session id is too long or contains illegal characters, valid characters are a-z, A-Z, 0-9 and '-,' in Unknown on line 0


Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/data/wwwroot/dede/data/sessions/) in Unknown on line 0 


我data/sessions/权限都是777了，也不行，望解答谢谢了

------解决方案--------------------
/data/wwwroot/dede/data/sessions 目录不存在或不可写