Php sessions problem

can´t know why it keeps giving me the same problem over and over again
Warning: session_start(): open(/tmp\sess_2f6b3d07d0bbbab6d4e822e868a2c8cb, O_RDWR) failed: No such file or directory (2) in c:\inetpub\wwwroot\magik\admin.php on line 11

Warning: session_start(): Cannot send session cookie - headers already sent by (output started at c:\inetpub\wwwroot\magik\admin.php:11) in c:\inetpub\wwwroot\magik\admin.php on line 11

Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at c:\inetpub\wwwroot\magik\admin.php:11) in c:\inetpub\wwwroot\magik\admin.php on line 11
user authentication using sessions


[ Record session data ] [ checks session ] [ logout ]

the data willl be recorded in the session.

session started !!

Warning: Unknown(): open(/tmp\sess_2f6b3d07d0bbbab6d4e822e868a2c8cb, O_RDWR) failed: No such file or directory (2) 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 (/tmp) in Unknown on line 0