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!:)