The block and media folder trees don't show up in the assets pane.

1. Go to admin view -> Config tab -> Manage Websites -> Websites tab.
2. Click the affected site.
3. Uncheck the Use site-specific assets box and click Save.
4. Go back to edit view. Make sure you can see the blocks and media folder trees in the assets pane.
5. Go back to admin view. Check the Use site-specific assets checkbox again and click Save.