Runtime error in scripts : CX_SY_DYN_CALL_PARAM_MISSING

Question

HI guys i am trying to print some values in sapscripts . 
the thing is i am able to see the print preview and the values are showing up  but when i click on the back button the system throws the following dump :
Runtime Errors         PERFORM_PARAMETER_MISSING
Except.                CX_SY_DYN_CALL_PARAM_MISSING
Short text
    Missing parameter with PERFORM.
What happened?
    Error in the ABAP Application Program
    The current ABAP program "RSNAST00" had to be terminated because it has
    come across a statement that unfortunately cannot be executed.
Error analysis
    An exception occurred that is explained in detail below.
    The exception, which is assigned to class 'CX_SY_DYN_CALL_PARAM_MISSING', was
     not caught in
    procedure "PROGRAMM_AUFRUFEN" "(FORM)", nor was it propagated by a RAISING
     clause.
    Since the caller of the procedure could not have anticipated that the
    exception would occur, the current program is terminated.
    The reason for the exception is:
    A PERFORM was used to call the routine "SHOW_VAL" of the program "Z_SHOWDATA".
    The current call contains 2 actual parameter(s),
    but the routine "SHOW_VAL" expects 4 parameters.
in the script this is the perform i ve written :
/:          PERFORM SHOW_VAL IN PROGRAM Z_SHOWDATA
/:          USING &NAST-OBJKY&
/:          CHANGING &VARIABLE4&
/:          CHANGING &VARIABLE5&
/:          CHANGING &VARIABLE6&
/:          ENDPERFORM
and my show_val goes as follows:
PROGRAM  Z_SHOWDATA.
data: var1 like NAST-OBJKY,
var3 type P decimals 2, "string , "decimals 2, " decimals 2,
var4 type p decimals 2, "string , "decimals 2, " decimals 2,
var5 type P decimals 2, "string, " decimals 2, "decimals 2,
var6 type p decimals 2.  "string .
data: itab type ekpo occurs 0 with header line .
form show_val tables intab structure itcsy
outab structure itcsy .
import sapscript parameters
read table intab with key 'NAST-OBJKY'.
check sy-subrc eq 0.
var1 = intab-value.
get Data
select single * into itab
from ekpo where EBELN eq var1.
select single *
       from ekpo
       into  itab
       where ebeln eq var1.
var3 = itab-netwr * 16 / 100.
var4 = var3 * 2 / 100.
var5 = var3 / 100.
var6 = itab-netwr + var4 + var5.
export sapscript parameters
READ TABLE outab WITH KEY 'VARIABLE4'.
CHECK sy-subrc EQ 0.
MOVE var4 TO outab-value.
condense outab-value.
append outab .
READ TABLE outab WITH KEY 'VARIABLE5'.
CHECK sy-subrc EQ 0.
MOVE var5 TO outab-value.
condense outab-value.
append outab .
READ TABLE outab WITH KEY 'VARIABLE6'.
CHECK sy-subrc EQ 0.
MOVE var6 TO outab-value.
condense outab-value.
append outab .
endform.
I am not able to catch the error in the code as all the values that i ve passed in the perform are successfully entered in the tables that i ve passed in my form . and the values are coming on the layout too
and the dump comes after i click on the back button after seeing the preview . Please help.
Vikram.
Please help

Answer 1

try like this and let me know if dump still exists, later we can do further analysis.
PROGRAM Z_SHOWDATA.
<b>*data: var1 like NAST-OBJKY,
*var3 type P decimals 2, "string , "decimals 2, " decimals 2,
*var4 type p decimals 2, "string , "decimals 2, " decimals 2,
*var5 type P decimals 2, "string, " decimals 2, "decimals 2,
*var6 type p decimals 2. "string .
data: var1(30),
var3 (30),
var4(30),
var5(30),
var6(30).</b>
data: itab type ekpo occurs 0 with header line .
form show_val tables intab structure itcsy
outab structure itcsy .
import sapscript parameters
read table intab with key 'NAST-OBJKY'.
check sy-subrc eq 0.
var1 = intab-value.
get Data
select single * into itab
from ekpo where EBELN eq var1.
select single *
from ekpo
into itab
where ebeln eq var1.
var3 = itab-netwr * 16 / 100.
var4 = var3 * 2 / 100.
var5 = var3 / 100.
var6 = itab-netwr + var4 + var5.
export sapscript parameters
READ TABLE outab WITH KEY 'VARIABLE4'.
CHECK sy-subrc EQ 0.
MOVE var4 TO outab-value.
condense outab-value.
append outab .
READ TABLE outab WITH KEY 'VARIABLE5'.
CHECK sy-subrc EQ 0.
MOVE var5 TO outab-value.
condense outab-value.
append outab .
READ TABLE outab WITH KEY 'VARIABLE6'.
CHECK sy-subrc EQ 0.
MOVE var6 TO outab-value.
condense outab-value.
append outab .
endform.
Regards,
SaiRam