Input paremeter for Uri.TryCreate, Whats wrong?

We have few downloaded HTML pages, with broken links (relative paths), and we have the original URL each page was downloaded from. We are converting all relative links to Absolute links using - Foreach (anchorElement in page) - Uri.TryCreate( originalPageURI, hrefRelativeURI, hrefAbsoluteURI ) This works for most of the cases except for the following case - originalPageURI =