session_start problem

[eluser]dimis[/eluser]
I have 2 models that have controls at php session variables.
So I extend model class as

Code:

class My_Model extends Model {  
    function My_Model()
    {
        parent::Model();
        @session_start();


    }
}

and the 2 models extends this class .
At my log file I see that

Code:

ERROR - 2008-11-05 12:44:05 --> Severity: Notice  -->
A session had already been started -
ignoring session_start() C:\xampp\htdocs\dslook\system\application\libraries\My_Model.php 7

.
Is there any problem with that and how can I solve it?