Microsoft EULA, Internet

Yesterday I called Microsoft because Silverlight said it was not compatible with Vista64.  I reported to the rep that was funny because the same OS on the same computer other boot partition did not have that complaint.  The rep then said in asking, so you have installed Vista under the same license on different boot partitions on same computer?  I said yes because in the wide world of hardware and software there are incompatibles.  He then said that was illegal under my EULA, and he (Microsoft and he) were going to, Cite Me.  Just what does that mean?