Membership.GetUser(UserName) returns null

this web app develop using asp.net 2.0 & MySQL 5.1. mysql membership & role providers use for forms authantication. it works fine in WinXP developer PC and Win2003 production server. but not working om my win7 PC & win 2008 R2 server
 
protected void Login1_LoggedIn(object sender, EventArgs e)
{
        MembershipUser mu = Membership.GetUser(Login1.UserName); // this return Null

        if (mu.IsApproved)
        { ///}
}
please help!!

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