Library /sys$common/syshlp/dbg$help.hlb DEBUG, Messages, NOSUCHDISP  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 no such display defined: display_name

    Facility: DEBUG, VMS Debugger

    Explanation: The specified display <display_name, !AC> does not
    exist.

    User Action: Re-enter the command, specifying an existing
    display.