get a date time exception when getting birthday from user?

Hi,
On my register.aspx page I am getting the birthday of the user in a create user wizard control.
and saving it in the asp.net profile
web Config


<profile enabled="true">
      <properties>
     
        <add name="Bday" type="System.DateTime" />
      </properties>
    </profile>

Register.aspx
 

<div>Your Birthday</div& ...