embedded pictures do not show anymore on Email coming in

hi
Strange enough. All of a sudden I cannot read all the pictures embedded in the emails I receive. Instead I can see a red cross in a small white window.
My system is XP pro 32 bits and I use Outlook2007.
I have been looking everywher in outlook, my Avast antivirus, firefox browser and several French forum since I live in France and could not find anybody with the same problem.
Hopefully somone will be wiser on your side of the Atlantic
Thank you in advance.
Patrick