public bool isLoggedIn()
{
    return System.Web.HttpContext.Current.User.Identity.IsAuthenticated;
}

public void Login_OnClick(object sender, EventArgs args)
{
    string email = UserName.Text;
    string password = Password.Text;
    string errorMsg = string.Empty;
    bool cb = cb_agreeterms.Checked;

if (tests)
    {
        // The code in here tests to see if email, password, etc. have been filled out.
        //  This works 100% of the time and is NOT a problem.
    }
    else
    {
        // Validate user.
        if (Membership.ValidateUser(email, password))
        {
            // Get the logged in user
            MembershipUser user = Membership.GetUser(email);

            if (user.IsLockedOut)
            {
                user.UnlockUser();
            }

    // Gets a datatable of the user details in our general database
            DataTable dtUserData = this.dbData.GetUserByEmail(user.UserName);

            if (dtUserData.Rows.Count > 0)
            {
                FormsAuthentication.SetAuthCookie(user.UserName, true);

                // The details for the userId, screenName, etc. below get set by looking at the row 0 in datatable

        // The LoginSession function intializes a session with a guid and saves all the data into an Application Context. This creates a SessionGuid cookie which I see get created on FF and Chrome (and always on IE).
                LoginSession(userId, screenName, permissionLevel, user.UserName);

                Response.Redirect("../myinternalsite.aspx");
            }
        }
        else if (UserExistsInMembership(email))
        {
            // Tested this out and entering bad credentials fails the login and error is shown correctly on screen in the login control.

            // We have failed to login.
            ShowLoginError("E-mail or password is incorrect.");
        }
    }
}

public bool isLoggedIn()

// authenticationConnection works and links correctly to the auth database just fine.
<sessionState timeout="120"/>

<membership defaultProvider="SqlProvider">

    <providers>

        <add connectionStringName="authenticationConnection" applicationName="Auth" minRequiredPasswordLength="6" minRequiredNonalphanumericCharacters="0" name="SqlProvider" type="System.Web.Security.SqlMembershipProvider" requiresQuestionAndAnswer="false" passwordFormat="Hashed" enablePasswordReset="true" maxInvalidPasswordAttempts="1000" passwordAttemptWindow="1" />

    </providers>

</membership>

<roleManager enabled="true" defaultProvider="SqlRoleManager">

    <providers>

        <add name="SqlRoleManager" type="System.Web.Security.SqlRoleProvider" connectionStringName="authenticationConnection" applicationName="MyApp"/>

    </providers>

</roleManager>

<identity impersonate="true"/>