ERROR: invalid input syntax for integer: SQL state: 22P02

hi guys,
i am new to pgsql and i am facing a strange problem which i cannot solve.i
want to import data from a txt file to the table cust

the table is
CREATE TABLE cust
(
custid integer NOT NULL,
custOccupation varchar(30) NOT NULL,
PRIMARY KEY(custid)
}

and the txt file contains
13;developer
22;sales manager
etc

i issue the following sql command
COPY cust
FROM 'C:\Program Files\PostgreSQL\9.1\customers.txt'
WITH DELIMITER ';' ;

and i get an error
ERROR: invalid input syntax for integer: "13"
SQL state: 22P02

i would appreciate if you could help me

best regards and a happy new year!:)