Assets and MSM won't upload/display

Question

I have sites A and B Each site has it's own uploads directory, and I have the upload preferences set dynamically:

$config['upload_preferences'] = array(
        1 => array(                                                            // ID of upload destination
            'name'        => 'A Images',                          // Display name in control panel
            'server_path' => $_SERVER['DOCUMENT_ROOT'] . '/files/uploads/', // Server path to upload directory
            'url'         => '/files/uploads/'      // URL of upload directory
        ),
        2 => array(                                                            // ID of upload destination
            'name'        => 'B Images',                          // Display name in control panel
            'server_path' => $_SERVER['DOCUMENT_ROOT'] . '/files/uploads/', // Server path to upload directory
            'url'         => '/files/uploads/'      // URL of upload directory
        )
    );

so if you are logged into the individual MSM sites control panel (a.com/admin.php), you should be able to upload images to that relative path. I can upload them to the folder via FTP, and then index them via assets and they become available to select, but the thumbnails do not show up. so 2 issues:

1. I can't upload on sibling MSM sites using their respective document roots for upload paths
2. When viewing files that are indexed in assets, no thumbnails appear in file browser

Answer 1

Have you looked at there possibly being problems with openbase_dir restrictions affecting that? I have generally found with MSM upload errors and images not working correctly have been due to openbase_dir restrictions.