Authentification on mac

Hi all,
i have on my w2003 server iis installed and paste my homepage with an domain windows authentification. On windows it runs without any problem. Unfortunatly the mac(safari) make trouble. Some user can't login on the site. But not all users have this problem with safari. I don't know really why?
I hope here are some pros who can help me or show me an alternative way to authentificate.
here is my web.config:
<authentication mode="Windows"/>
    <anonymousIdentification enabled="true"/>
    
    <authorization>
      
      <allow roles="domain\goup" />
      <deny users="*"/>
      
    </authorization>
 


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