and tried to apply a definition query on the census block layer. It works perfectly. So the problem might be my layer or something on the server. There is something that must be done on the layer in order to print it with a definition query?
Regards Marco
EDIT:
I've found the problem. I think it is a BUG of ArcGis Server.
The MapServer has enabled the option 'Allow per request modification of layer order and symbology'. After disabling it I can print with the layer definition.