There are many possible reasons for this but I'll suggest a few to see if they help.
First of all, when you create a document it is setup to display properly only for the default printer (or which ever printer is chosen in page setup at that time). These settings get saved along with the document and is a common cause of formatting mismatches when documents that were saved on one system for a particular printer setup are printed on a different system with a different printer setup. To fix this usually requires going into the page setup and choosing the right printer & settings for the document.
The next thing I would be checking is that both printers are using the same printer language, this is usually going to be either PS (PostScript) or PCL. Each language handles the drawing of graphics in a radically different way and while you may find the document will print fine in one it will turn out completely different in the other. As the waternark is sent to the printer as a graphic you may need to change the settings somewhere to tell it to use raster graphics for all drawing in the printer properties.
The following Microsoft article describes an unrelated problem but may also give you an idea of where to start looking.
http://support.microsoft.com/default...US;286902&FR=1