The content tree to the left of the admin dashboard does not work when using the legacy layer.

Looking at the network traffic, the request to content/treemenu/... returns a 500 Internal Server Error; through some poking around we've traced the origin of the error to line ~158 of index_treemenu.php:

if ( !$hasAccessToSite )
{
    exitWithInternalError();
    return;
}

The content tree works correctly if accessing the legacy installation directly (bypassing the symfony stack).