Biest,
What I suspect happened, is that when you uninstalled Silverlight, what was left behind was the receipt package. When you attempted to reinstall Silverlight, it detected the new (receipt/pkg) version and ergo your problem.
Try this:
Go to Computer/Library/Receipts folder and move to your desktop, all pkgs with the name: “Office2008_en_silverlight_ xxxxxx” (there may be several packages).
Restart your computer. This step my be unnecessary, I just don't know. But it can't hurt.
Then try reinstalling Silverlight. If all is well, those packages you moved to your desktop may be deleted. Otherwise, return them whence they came.
Again, do not trash those Receipt pkgs on the desktop until you are sure all is well.