It kind of sounds like it's getting modified somehow. I assume you've tried to print out the file, or at least the start of it? If it could be some kind of non-printable stuff, I'd read the file in to a byte array and print out the first several bytes to see if you can figure out what's getting added/modified by the Comcast connection. Something like:
ba = CreateObject("roByteArray")
ba.ReadFile("tmp:/myfile")
for i = 0 to 10
print ba[i]
end for
For what it's worth, you'd probably be better off using a regular expression to extract the URL. It would be more flexible and wouldn't depend on some fixed offset.
-JT
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