new mail checking is not working

Hi Ehsan
when I try checking new mails It returns an empty value instead of 1 or 0.
so I check the content of outputfile ,
in file `class.GrabYahoo.php` on line : 590

I found that yahoo retuns an error message to this request
meaning that yahoo can not detect the browser

I cant understand what is the reason an what's wrong with the class
please do check this.
I'm waiting ...

thanks
E.Imami