Problem compiling a Cobol program reading from diskfile

I am trying to learn Cobol using Murachs Mainframe Cobol book and GNUCobol 3.1 compiler. Currently I am stuck at Chapter 3, where I am suppose to read from a disk file and generate a report.

I have placed the .dat file in same folder as where I compile the program (and also in a /bin folder in same directory).

When I try to compile the program I receive the following error:

rose@eden~/cobol/Programs/Chapter 03 $ cobc -x RPT1000.CBL 
RPT1000.CBL:11: error: redefinition of 'CUSTMAST'
RPT1000.CBL:11: error: 'CUSTMAST' previously defined here
RPT1000.CBL:12: error: redefinition of 'SALESRPT'
RPT1000.CBL:12: error: 'SALESRPT' previously defined here

Relevant Program code:

   IDENTIFICATION DIVISION.
  
   PROGRAM-ID. RPT1000.
  
   ENVIRONMENT DIVISION.
  
   INPUT-OUTPUT SECTION.
  
   FILE-CONTROL.
  
       SELECT CUSTMAST ASSIGN TO CUSTMAST.
       SELECT SALESRPT ASSIGN TO SALESRPT.
  
   DATA DIVISION.
  
   FILE SECTION.
  
   FD  CUSTMAST.
  
   01  CUSTOMER-MASTER-RECORD.
       05  CM-BRANCH-NUMBER        PIC 9(2).
       05  CM-SALESREP-NUMBER      PIC 9(2).
       05  CM-CUSTOMER-NUMBER      PIC 9(5).
       05  CM-CUSTOMER-NAME        PIC X(20).
       05  CM-SALES-THIS-YTD       PIC S9(5)V9(2).
       05  CM-SALES-LAST-YTD       PIC S9(5)V9(2).
  
   FD  SALESRPT.
  
   01  PRINT-AREA      PIC X(132).

Solution

  SELECT CUSTMAST ASSIGN TO "bin/CUSTMAST.dat".
  SELECT SALESRPT ASSIGN TO "bin/SALESRPT.dat".

Solved the problem ...