Windows to FBA conversion giving Access Denied error

1. In SP 2010, I have a web application, Default zone, which was configured using Windows authentication (on port 9991).

    This web application was extended on Intranet zone (on port 9992).

2. I enabled the Claims based authentication on Default zone web application (port 9991), by using following:

          $webApp = Get-SPWebApplication "http://myserver:9991"
          $webApp.UseClaimsAuthentication = $True;
          $webApp.Update();

3. From IIS settings of site on port 9991, I have configured the "Connection Settings" and "Providers" (Role & Membership provider). Then from Central Admin, for my Default zone (9991) web application Authentication Providers, I have enabled the "Form Based Authentication" using my Role provider and Membership provider. And here I selected the default Sign-In page.

4. Using System account, I have given the permission to a windows user account. Now when I login using this new windows user account, I am getting "Access Denied" error in both zones (port 9991 & 9992). Whatever permission I give (Full access, Contribute or Read), it is always giving the same error.

5. Now when I do the "MigrateUser($True)" for Default zone web application, this solves the problem.

Is there any solution, so that without using the MigrateUser($True) command, I should be able to login using the normal Windows user account.