profile 问题～～


MembershipUser user = Membership.CreateUser(strUserName, strPwd, txtMail.Text.Tri());     
order.OrderId = Guid.NewGuid();
order.OrderDate = DateTime.Now;
...ProfileCommon profile = Profile.GetProfile(user.UserName);
                   
Profile.title = ddpTitle.SelectedItem.Text;
Profile.birthday = ddpDay.SelectedItem.Text + "-" + ddpMonth.SelectedItem.Text + "-" + ddpYear.SelectedItem.Text;
Profile.houseno = txtHouseNo.Text;
Profile.postcode = TxtPostCode.Text;
...<profile>
       <properties>
         <add name ="title" type="string"/>
         <add name ="birthday" type="string"/>
         <add name="houseno"  type="string"/>
         <add name="postcode" type ="string"/>
         <add name ="address1" type="string"/>
         <add name ="address2" type="string"/>
         <add name ="address3" type="string"/>
         <add name ="address4" type="string"/>
         <add name ="mobileTel"  type="string"/>
         <add name ="daytimeTel" type="string"/>
         <add name ="email" type ="string"/>
       </properties>
     </profile>问题：当Profile.title = ddpTitle.SelectedItem.Text; 时异常：{"This property cannot be set for anonymous users."}　
请教？