I'm unsure why the Error Checker tool can load that page. However, I just manually checked your page for all the issues that the automated checker would search for and there is nothing it would have caught. I'd suggest skipping that check and move on to configuration and testing, as it sounds like you have.
As for getting the user_posts (or any other permission), usually going through the app review isn't required. When setting up a channel, most of the time, the 'owner' of the Facebook Page is also an admin of your Facebook app.. and usually, that person is 'you'. If that's the case on your site and you don't plan to setup channels for other Facebook Pages and users on your site that aren't admins of your Facebook app, then you can skip the review process by doing the following:
* Go to the Facebook Developer area
* Set your app into "Development Mode" (sometimes this is switching the "Live" button to 'No')
* Then, after you've setup the channel, authenticate on your site. You should be prompted for all the permissions the channel needs.
* Once granted, you can change your app back to Live mode
From there, your user will already have granted the proper permissions and your site will be accessible to normal users who need the more basic permissions to authenticate.
I hope that helps, but if you need anything else, please let us know.
Thanks,
Alex