the problem is here:
Warning: session_start() [function.session-start]: open(/tmp\sess_e2c9fa410edeba3a0c29054395668806, O_RDWR) failed: No such file or directory (2) in d:\wwwroot\web2\valida_senha.php on line 28
The location of session files must be \tmp\sess_e2c9fa410edeba3a0c29054395668806 not /tmp\sess_e2c9fa410edeba3a0c29054395668806.
I think there is an error in php configuration file, the one that tells where sessions are kept.
Mine looks like that
Hope I am right.
rest of errors appear because there was an message sent before the session starts.