Error Code: 1193. Unknown system variable 'lastmodified' 0.000 sec from converted datetime in mysql workbench

Question

I have a hard time loading the data below with datetime into mysql workbench. The system always flag out "Error Code: 1193. Unknown system variable 'lastmodified' 0.000 sec". It would great if anyone can help me out. Thanks!

Here is my data:

id  categoryname        categoryorder   categorytype    lastmodified    lastmodby
1   Company Information 0   Articles    8/6/2002 0:00   
2   Checkout Process    0   Articles    8/6/2002 0:00   
3   Home / Welcome Pages    0   Articles    8/6/2002 0:00   
4   Affiliate System    0   Articles    8/6/2002 0:00   
5   Order Finished      0   Articles    8/6/2002 0:00   
6   Other Articles      0   Articles    8/6/2002 0:00   
7   Sample Articles     0   Articles    8/6/2002 0:00   
8   Reserved For Future Use 0   Articles    8/6/2002 0:00   
9   Order Status        10  Help    3/25/2016 16:36 7
10  Shipping and Delivery   20  Help    3/25/2016 10:58 7
11  Returns/Return Policy   30  Help    3/25/2016 10:11 7
12  Defective/Flawed Products   40  Help    3/25/2016 10:12 7
13  Affiliate/Distributor   50  Help    3/25/2016 10:59 7
14  Pricing and Billing 60  Help    3/25/2016 11:00 7
17  Guarantees      90  Help    3/25/2016 10:14 7
19  Donations       0   Articles        
20  Additional Support  232 Help    3/25/2016 10:14 7

Here is my codes:

CREATE TABLE articlecategories (
id INT NOT NULL AUTO_INCREMENT,
categoryname TEXT,
categoryorder INT NOT NULL,
categorytype VARCHAR(126),
lastmodified DATETIME,
lastmodby TEXT,
PRIMARY KEY (id)
) ENGINE InnoDB;


LOAD DATA INFILE "path/articlecategories.csv"
INTO TABLE ArticleCategories
FIELDS TERMINATED by ',' ENCLOSED BY '\"'
LINES TERMINATED BY '\r\n'
IGNORE 1 LINES
(id, categoryname, categoryorder, categorytype, @lastmodified, lastmodby);
SET lastmodified = STR_TO_DATE(@lastmodified, '%m/%d/%Y %H:%i');