You attempted to redefine a previously defined register symbol with
 a different value.

    Warning: You are attempting to change the definition of a
    register symbol that either you have previously defined or that
    MACRO-64 has predefined.

    User Action: Check for conflicts with the register-symbol
    identifier you have specified. If you wish to redefine a register
    symbol, you must first cancel its previous definition with the
    .UNDEFINE_REG directive.