i have a problem with my admin page please help.

hi

i cant click on anything on my admin page showing big
( permission denied)!!
and on top
Notice: unserialize() [function.unserialize]: Error at offset 2708 of 5536 bytes in /home/bnjtradi/public_html/system/library/user.php on line 23Warning: Invalid argument supplied for foreach() in /home/bnjtradi/public_html/system/library/user.php on line 23

please help me and thank you in advance
sokanso

and when i try to log out from opencart admin page it show this message

Notice: unserialize() [function.unserialize]: Error at offset 2708 of 5536 bytes in /home/bnjtradi/public_html/system/library/user.php on line 23Warning: Invalid argument supplied for foreach() in /home/bnjtradi/public_html/system/library/user.php on line 23Warning: Cannot modify header information - headers already sent by (output started at /home/bnjtradi/public_html/admin/index.php:69) in /home/bnjtradi/public_html/system/engine/controller.php on line 27

any one could show me how to fix it??
thanks
sokanso