the debugger will be unable to create a separate window; UIS too
 old.

    Facility: DEBUG, VMS Debugger

    Explanation: The debugger requires VWS V3.0 or later to create a
    separate window (see SET MODE SEPERATE).

    User Action: To allow the debugger to create a separate window,
    install VWS V3.0 or later, and in your private startup file (or
    at DCL), DEFINE/SYSTEM UIS$VT_ENABLE_OSC_STRINGS TRUE.