/sys$common/syshlp/helplib.hlb OPEN, Qualifiers, /ERROR  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /ERROR=label

    Transfers control to the location specified by the label keyword
    (in a command procedure) if the open operation results in an
    error. The error routine specified for this qualifier overrides
    any ON condition action specified. If the /ERROR qualifier is not
    specified, the current ON condition action is taken.

    If an error occurs and the target label is successfully given
    control, the global symbol $STATUS retains the code for the error
    that caused the error path to be taken.