Hi,
In the actual book example you do not need the ~, although you might well do for your own site.
If you point it at the ProductImages directory as follows:
Eval("PictureURL","ProductImages/thumb_{0}")
then it works fine for me using the Begin/Chapter13 code. It depends on the structure and setup of your own particular site.
Chris
Chris Ullman
Programmer/Technical Author
http://www.cuasp.co.uk