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

 mask operations not allowed on record and SCAN tree objects

    Facility: DEBUG, VMS Debugger

    Explanation: A mask operation (as specified by the /TMASK or
    /FMASK qualifiers) cannot be performed on a record or SCAN tree
    object.

    User Action: Specify an array or address range to perform the
    mask operation on.