Updating Cubase 5

I have downloaded Cubase_5.5.0_update from the Steinberg wbsite, but it will not load and update my current versio (5.1.1). I am running Windows XP pro SP3, and hope to upgrade to Windows 7 64 bit very soon. Can anyone suggest why it will not load? Is it perhaps incompatible with what I have?

Is your eLicenser updated to the latest version?