Hi Mike,
Is this a folder based child site or a site running in a virtual directory or a root level site?
You should not be using extra / segments in your friendly urls, it is not supported. You can use - but not /
But my guess is that you have this set to true and you have extra / segments
<add key="UseFoldersInsteadOfHostnamesForMultipleSites" value="true" />
so it is trying to resolve the extra segment as a site folder in a multi site installation.
Hope it helps,
Joe