Inserting Table Data Into A Variable

I am trying to insert a column into a variable from a trigger.

Here is the code that i have:

CREATE OR REPLACE TRIGGER BUYER_after_update AFTER UPDATE ON buyer
FOR EACH ROW
DECLARE
v_key varchar2(10);
BEGIN
select ID into v_key from buyer;
insert into message_log_table (table_name, message_comments)
values
('Buyer', 'Buyer '||v_key||' has been updated');
end;
/

When I run the above I get the following compiler error:

[Error] ORA-00904 (6: 12): PL/SQL: ORA-00904: "ID": invalid identifier

Since ID is defined in my BUYER table I do not understand what the error means.

Here is my create table statement:

CREATE TABLE BUYER
(
ID VARCHAR(50) NOT NULL PRIMARY KEY,
FNAME VARCHAR(50) NOT NULL,
LNAME VARCHAR(50) NOT NULL,
ADDRESS VARCHAR(50) NOT NULL,
CITY VARCHAR(50) NOT NULL,
STATE VARCHAR(2) NOT NULL,
ZIP_CODE NUMBER(5) NOT NULL
);