I'm having problems with forms authentication using a SQL Server data store. I can log in successfully, but get returned immediately to the login page. After putting some code in my login form for diagnostic purposes I've found that Membership.ValidateUser will return True (so I assume that validation against the stored user name and password is working okay), but User.Identity.IsAuthenticated returns False.

What am I doing wrong here? In case it helps, here is the relevant section from Web.config:

  <authentication mode="Forms">
       <forms name="SqlAuthCookie" timeout="10" />
  </authentication>
        <authorization>
            <deny users="?"/>
            <allow users="*"/>
        </authorization>
        <membership defaultProvider="MySqlMembershipProvider">
            <providers>
                <clear/>
                <add name="MySqlMembershipProvider"
            connectionStringName="ACONConnectionString"
            applicationName="aconclients"
            type="System.Web.Security.SqlMembershipProvider"
            minRequiredPasswordLength="5"
            minRequiredNonalphanumericCharacters="0"
            passwordAttemptWindow="10"
            passwordStrengthRegularExpression=""/>
            </providers>
        </membership>

Any help would be much appreciated.