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

 register required in context for operand number operand_number

    Facility: DEBUG, VMS Debugger

    Explanation: A register is required to establish context for the
    specified operand.

    User Action: If the instruction was entered by the user, reenter
    the instruction, using a register with the specified operand. If
    not, then there may be an error in the user program instructions.