Argument N is invalid. The assembler failed to find a base register
 specified with a previous .BASE directive to form a register
 expression of the form offset(Rn).

    Error: The assembler could not find a base register, which
    you specified with a previous .BASE directive, to form a valid
    register expression of the form offset(Rn).

    User Action: Check the instruction in the source code and see the
    description of the .BASE directive.