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That probably means you have an "XU" account which is for facility users for LCLS systems.  XU accounts do not have access to central computing systems (they do not have a valid shell on central computing systems).  If your status has changed from a facility users to a staff user, then you can request to have your group changed from XU to XRsomething else, so you have access to central computing systems, such as FastX.  You can contact ithelp@slac.stanford.edu for help changing your account status.

Connecting to FastX using your Web Browser

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