MS Outlook 2007 (12.0.6316.5000)

There was no problem with images downloading in HTML emails. A couple days
ago Outlook stopped downloading images without any configuration change.
When I manually right click and select downloading images or even unblock it
globally I can see only placeholders for images (red 'x' sign in the
square). The same emails on another machine are displayed properly.
Sometimes I can see some images (two or free) but the rest of them aren't
displayed. What can cause the problem?

Jacek