GUI_UPLOAD --> file doen't exist

Hi experts,

I am new at SAP, i am writing a program the upload a CSV (i had previosly created and saved in CSV format)  file in a SAP internal table using GUI_UPLOAD as you can see below.

When i execute, the program says: "file doens't exist".

REPORT: ztest_005.

TABLES: zfi_employee2.

DATA: ls_zfi_tab1 TYPE zfi_employee2,
      lt_zfi_tab1 LIKE ls_zfi_tab1 OCCURS 0 WITH HEADER LINE,
      i_text_data LIKE STANDARD TABLE OF zfi_employee2,
      Upload TYPE string.

*PARAMETERS: p_file TYPE rlgrap-filename OBLIGATORY.

AT SELECTION-SCREEN ON VALUE-REQUEST FORp_file.
  CALL FUNCTION'KD_GET_FILENAME_ON_F4'
       EXPORTING
            static    = 'X'
       CHANGING
            file_name = p_file.

START-OF-SELECTION.

Upload = 'p_file'.


CALL FUNCTION 'GUI_UPLOAD'
  EXPORTING
    filename                      = Upload
   FILETYPE                      = 'ASC'
   HAS_FIELD_SEPARATOR           = ' '
*   HEADER_LENGTH                 = 0
*   READ_BY_LINE                  = 'X'
*   DAT_MODE                      = ' '
*   CODEPAGE                      = ' '
*   IGNORE_CERR                   = ABAP_TRUE
*   REPLACEMENT                   = '#'
*   CHECK_BOM                     = ' '
*   VIRUS_SCAN_PROFILE            =
*   NO_AUTH_CHECK                 = ' '
* IMPORTING
*   FILELENGTH                    =
*   HEADER                        =
  tables
    data_tab                      =  i_text_data
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.

CALL FUNCTION 'TEXT_CONVERT_XLS_TO_SAP'
  EXPORTING
   I_FIELD_SEPERATOR          = ' '
*   I_LINE_HEADER              =
    i_tab_raw_data             = i_text_data
    i_filename                 = p_file
  tables
    i_tab_converted_data       = lt_zfi_tab1
EXCEPTIONS
   CONVERSION_FAILED          = 1
   OTHERS                     = 2
          .
IF sy-subrc <> 0.
MESSAGE ID SY-MSGID TYPE SY-MSGTY NUMBER SY-MSGNO
         WITH SY-MSGV1 SY-MSGV2 SY-MSGV3 SY-MSGV4.
ENDIF.

LOOP AT lt_zfi_tab1 INTO ls_zfi_tab1.
WRITE: /5 ls_zfi_tab1-sct.
WRITE:21 ls_zfi_tab1-wrk.
WRITE:41 ls_zfi_tab1-tpwrk.
WRITE:61 ls_zfi_tab1-mnsn.
CLEAR ls_zfi_tab1.
ENDLOOP.

Could anyone help me? Thanks