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

 illegal sign extension field value extension_value

    Facility: DEBUG, VMS Debugger

    Explanation: An illegal value has been entered for the sign
    extension field in a field reference.

    User Action: Re-enter the command using a valid sign extension
    field value.