Can't login with root at Runlevel 3

i used init 3 to move to runlevel 3 , but after I can't login with root password , i viewed the the file "/var/log/secure" and found this :

Quote:

Jun 25 17:39:12 localhost login: pam_unix(login:auth): authentication failure; logname=LOGIN uid=0 euid=0 tty=tty1 ruser= rhost= user=root Jun 25 17:39:13 localhost login: FAILED LOGIN SESSION FROM (null) FOR root, Permission denied

what could be the issue ?

Note: when i boot the system normally and the graphical login user interface appear and i use the same credentials , it login normally ,so the problem only occur when changing to another runlevel from the terminal .

Note2: I'm using Centos

Regards