CrystalReportViewer buttons don"t display

I have a CrystalReportViewer control on an aspx page, 2.0 framework.
The report itself displays correctly, but all the images on buttons
(Print, Export, record navigation, etc) are not visible - they are
x'ed out... Does anyone know why this is? Am I missing a DLL? Here's
my declaration:

DisplayToolbar="True" DisplayGroupTree="false" />