devoloping the BDC For material schedule update for me38 but gives the error :-BDC_INSERT, session not opened

report ZBDC_ME38
        no standard page heading line-size 255.
*include bdcrecx1.
*parameters: dataset(132) lower case.
*** DO NOT CHANGE - the generated data section - DO NOT CHANGE    ***
*
*   If it is nessesary to change the data section use the rules:
*   1.) Each definition of a field exists of two lines
*   2.) The first line shows exactly the comment
*       '* data element: ' followed with the data element
*       which describes the field.
*       If you don't have a data element use the
*       comment without a data element name
*   3.) The second line shows the fieldname of the
*       structure, the fieldname must consist of
*       a fieldname and optional the character '_' and
*       three numbers and the field length in brackets
*   4.) Each field must be type C.
*
*** Generated data section with specific formatting - DO NOT CHANGE  ***

DATA: file_path TYPE string.

DATA: I_BDCDATA LIKE BDCDATA OCCURS 0 WITH HEADER LINE.
*
data: begin of record OCCURS 0,
         EVRTN_001(010),
         EBELP_002(005),
         ETNR1_003(004),
         LPEIN_04_004(001),
         EEIND_04_005(010),
         MENGE_04_006(017),
       end of record.


START-OF-SELECTION.


   SELECTION-SCREEN BEGIN OF BLOCK mode WITH FRAME TITLE text-003.

   PARAMETERS: file_url TYPE  rlgrap-filename MODIF ID xyz .

   SELECTION-SCREEN END OF BLOCK mode .

*PARAMETERS: dataset(132) lower case.
*perform open_dataset using dataset.
*Uploading data from the local file C:\MSchedule.txt
*CALL FUNCTION 'WS_UPLOAD'
* EXPORTING
*   FILENAME                      = 'C:\MSCHEDULE.TXT'
*   FILETYPE                      = 'DAT'
*  TABLES
*    data_tab                      = I_BDCDATA .
*
*IF sy-subrc <> 0.
* MESSAGE ID SY-MSGID TYPE SY-MSGTY NUMBER SY-MSGNO
*         WITH SY-MSGV1 SY-MSGV2 SY-MSGV3 SY-MSGV4.
*ENDIF.



AT SELECTION-SCREEN ON VALUE-REQUEST FOR file_url.
   CALL FUNCTION 'F4_FILENAME'
     EXPORTING
       program_name  = syst-cprog
       dynpro_number = syst-dynnr
       field_name    = 'FILE_URL'
     IMPORTING
       file_name     = file_url.

   start-of-selection.

   IF NOT file_url IS INITIAL.

     MOVE  file_url TO file_path.
     PERFORM read_file.
   ENDIF.


perform open_group.
perform close_group. "Closing the BDC session
LOOP AT RECORD. "Filling the BDC table with data

*read dataset dataset into record.

perform bdc_dynpro      using 'SAPMM06E' '0205'.
perform bdc_field       using 'BDC_CURSOR'
                               'RM06E-EVRTN'.
perform bdc_field       using 'BDC_OKCODE'
                               '/00'.
perform bdc_field       using 'RM06E-EVRTN'
                               record-EVRTN_001.
perform bdc_dynpro      using 'SAPMM06E' '0222'.
perform bdc_field       using 'BDC_CURSOR'
                               'EKPO-EMATN(01)'.
perform bdc_field       using 'BDC_OKCODE'
                               '=ET'.
perform bdc_field       using 'RM06E-EBELP'
                               record-EBELP_002.
perform bdc_dynpro      using 'SAPMM06E' '1117'.
perform bdc_field       using 'BDC_CURSOR'
                               'EKET-MENGE(04)'.
perform bdc_field       using 'BDC_OKCODE'
                               'BU'.
perform bdc_field       using 'RM06E-ETNR1'
                               record-ETNR1_003.
perform bdc_field       using 'RM06E-LPEIN(04)'
                               record-LPEIN_04_004.
perform bdc_field       using 'RM06E-EEIND(04)'
                               record-EEIND_04_005.
perform bdc_field       using 'EKET-MENGE(04)'
                               record-MENGE_04_006.
perform bdc_dynpro      using 'SAPLSPO1' '0300'.
perform bdc_field       using 'BDC_OKCODE'
                               '=YES'.
perform bdc_transaction using 'ME38'.
ENDLOOP.



FORM read_file .
   CALL FUNCTION 'GUI_UPLOAD'
     EXPORTING
       filename                      = file_path
      filetype                       = 'ASC'
      has_field_separator            = 'X'
*   HEADER_LENGTH                 = 0
      read_by_line                   = 'X'
*   DAT_MODE                      = ' '
*   CODEPAGE                      = ' '
*   IGNORE_CERR                   = ABAP_TRUE
*   REPLACEMENT                   = '#'
*   CHECK_BOM                     = ' '
* IMPORTING
*   FILELENGTH                    =
*   HEADER                        =
     TABLES
       data_tab                      = record
* EXCEPTIONS
*   FILE_OPEN_ERROR               = 1
*   FILE_READ_ERROR               = 2
*   NO_BATCH                      = 3
*   GUI_REFUSE_FILETRANSFER       = 4
*   INVALID_TYPE                  = 5
*   NO_AUTHORITY                  = 6
*   UNKNOWN_ERROR                 = 7
*   BAD_DATA_FORMAT               = 8
*   HEADER_NOT_ALLOWED            = 9
*   SEPARATOR_NOT_ALLOWED         = 10
*   HEADER_TOO_LONG               = 11
*   UNKNOWN_DP_ERROR              = 12
*   ACCESS_DENIED                 = 13
*   DP_OUT_OF_MEMORY              = 14
*   DISK_FULL                     = 15
*   DP_TIMEOUT                    = 16
*   OTHERS                        = 17
             .
   IF sy-subrc <> 0.
* MESSAGE ID SY-MSGID TYPE SY-MSGTY NUMBER SY-MSGNO
*         WITH SY-MSGV1 SY-MSGV2 SY-MSGV3 SY-MSGV4.
   ENDIF.

ENDFORM.                    " read_file



*perform close_dataset using dataset.
FORM OPEN_GROUP.
CALL FUNCTION 'BDC_OPEN_GROUP'
EXPORTING
CLIENT = SY-MANDT
GROUP = 'SESSION1'
USER = SY-UNAME
KEEP = 'X'.
IF SY-SUBRC <> 0.
WRITE 'ERROR IN OPEN_GROUP'.
ENDIF.
ENDFORM.

FORM BDC_DYNPRO USING PROGRAM DYNPRO.
CLEAR I_BDCDATA.
I_BDCDATA-PROGRAM = PROGRAM.
I_BDCDATA-DYNPRO = DYNPRO.
I_BDCDATA-DYNBEGIN = 'X'.
APPEND I_BDCDATA.
ENDFORM.

FORM BDC_FIELD USING FNAM FVAL.
CLEAR I_BDCDATA.
I_BDCDATA-FNAM = FNAM.
I_BDCDATA-FVAL = FVAL.
APPEND I_BDCDATA.
ENDFORM.

FORM BDC_TRANSACTION USING TCODE.
CALL FUNCTION 'BDC_INSERT'
EXPORTING TCODE = TCODE
TABLES DYNPROTAB = I_BDCDATA.
ENDFORM.

FORM CLOSE_GROUP.
CALL FUNCTION 'BDC_CLOSE_GROUP'.
ENDFORM. " CLOSE_GROUP