Runtime error in functional module

Question

they given below program is a function module calling program.while am execute this program they could display the message like as
What happened?
    Error in ABAP application program.
    The current ABAP program "YSUSFUN1" had to be terminated because one of the
    statements could not be executed.
    This is probably due to an error in the ABAP program.
    In program "SAPLYGROUP3 ", the following syntax error occurred
    in the Include "LYGROUP3U01 " in line 1:
    "The main program of the function "Y_INTERNAL1" does not begin with "FU"
    "NCTION-POOL"."
    Author and last person to change the Include are:
    Author "BASIS "
    Last changed by "BASIS "
Error analysis
    In program "SAPLYGROUP3 ", the following syntax error occurred:
    "The main program of the function "Y_INTERNAL1" does not begin with "FU"
    "NCTION-POOL"."
REPORT  YSUSFUN1.
TABLES YSUSTAB1.
DATA IT1 LIKE YSUSTAB1 OCCURS 2 .
SELECT * FROM YSUSTAB1 INTO TABLE IT1.
LOOP AT IT1 INTO YSUSTAB1.
WRITE: / YSUSTAB1-NAME, YSUSTAB1-ROLLNO,YSUSTAB1-PHONENO.
ENDLOOP.
CALL FUNCTION 'Y_INTERNAL1'
  TABLES
    IT4           =  IT1  .
    LOOP AT IT1 INTO YSUSTAB1.
    WRITE: / YSUSTAB1-NAME, YSUSTAB1-ROLLNO, YSUSTAB1-PHONENO.
    ENDLOOP.
2.)
the given below program is function module definition. while at that time of execution they could display the message as
*Syntax error in program*
*Source code   LYGROUP3U01                                    Line     1*
  *The main program of the function "Y_INTERNAL1" does not begin with*
  *"FUNCTION-POOL".*
FUNCTION Y_INTERNAL1.
""Local Interface:
*"  TABLES
*"      IT4 STRUCTURE  YSUSTAB1
LOOP AT IT4.
WRITE : IT4-name, it4-phoneno, it4-rollno.
endloop.
ENDFUNCTION.

Answer 1

thanks
before am gone to se80 to activate the function group , am  activate the function module only  not activate the function group .
now am activate the function group they could not be depict the error .