[REBOL] another upgrade problem

[subhra]

when i try to upgrade rebol it gave me this error ...
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"connecting to: www.rebol.com
** User Error: Error.  Target url: http://www.rebol.com/releases.html
could not be retrieved.  Server response: HTTP/1.0 407 Proxy
Authentication Required.
** Where: do http://www.rebol.com/releases.html"
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how do i specify proxy-user and proxy-passwd??
subhro.