When is a string not a string? (or something)

I'm not sure how to explain this because I've been banging my head against the wall for hours and I'm getting kind of delerious. :) 
What I'm trying to do is simple, I think - I'm scraping a string from a webpage.  That string is a url to an image.  I'm then using the following code to attempt to save that image:
sub saveimage(strURL as String, strFilename as String)
Dim client As New WebClient
strFilename = Server.MapPath(strFilename)
client.DownloadFile(strURL, strFilename)
client=nothing
end sub

This all works perfectly when I hardcode strFilename.  When I pull the string from the html stream and pass it to that sub however, the file that gets saved has zero bytes.  I think the string that's getting passed in is encoded in some way that is causing a problem.



Here's the part of the code t ...