Hello David,
The problem is with the DO statement.
If you remove it the datasource will work just fine.
| data: i_cont type int4, i_venum type venum, i_matnr type matnr. |
| data: wa_pallets TYPE zita_pallets. |
| * Auxiliary Selection criteria structure |
| DATA: L_S_SELECT TYPE SRSC_S_SELECT. |
| * Maximum number of lines for DB table |
| STATICS: S_S_IF TYPE SRSC_S_IF_SIMPLE, |
| * counter |
| S_COUNTER_DATAPAKID LIKE SY-TABIX, |
| * cursor |
| S_CURSOR TYPE CURSOR. |
| * Select ranges |
| * RANGES: L_R_CARRID FOR ZITA_PALLETS-CARRID, |
| * L_R_CONNID FOR ZITA_PALLETS-CONNID. |
| * Initialization mode (first call by SAPI) or data transfer mode |
| * (following calls) ? |
| IF I_INITFLAG = SBIWA_C_FLAG_ON. |
| ************************************************************************ |
| * Initialization: check input parameters |
| * buffer input parameters |
| * prepare data selection |
| * Check DataSource validity |
| CASE I_DSOURCE. |
| WHEN 'ZITA_PALLETS'. |
| WHEN OTHERS. |
| IF 1 = 2. MESSAGE E009(R3). ENDIF. |
| * this is a typical log call. Please write every error message like this |
| LOG_WRITE 'E' "message type |
| 'R3' "message class |
| '009' "message number |
| I_DSOURCE "message variable 1 |
| ' '. "message variable 2 |
| RAISE ERROR_PASSED_TO_MESS_HANDLER. |
| ENDCASE. |
| APPEND LINES OF I_T_SELECT TO S_S_IF-T_SELECT. |
| * Fill parameter buffer for data extraction calls |
| S_S_IF-REQUNR = I_REQUNR. |
| S_S_IF-DSOURCE = I_DSOURCE. |
| S_S_IF-MAXSIZE = I_MAXSIZE. |
| * Fill field list table for an optimized select statement |
| * (in case that there is no 1:1 relation between InfoSource fields |
| * and database table fields this may be far from beeing trivial) |
| APPEND LINES OF I_T_FIELDS TO S_S_IF-T_FIELDS. |
| ELSE. "Initialization mode or data extraction ? |
| * Data transfer: First Call OPEN CURSOR + FETCH |
| * Following Calls FETCH only |
| * First data package -> OPEN CURSOR |
| IF S_COUNTER_DATAPAKID = 0. |
| * Fill range tables BW will only pass down simple selection criteria |
| * of the type SIGN = 'I' and OPTION = 'EQ' or OPTION = 'BT'. |
| * LOOP AT S_S_IF-T_SELECT INTO L_S_SELECT WHERE FIELDNM = 'CARRID'. |
| * MOVE-CORRESPONDING L_S_SELECT TO L_R_CARRID. |
| * APPEND L_R_CARRID. |
| * ENDLOOP. |
| * |
| * LOOP AT S_S_IF-T_SELECT INTO L_S_SELECT WHERE FIELDNM = 'CONNID'. |
| * MOVE-CORRESPONDING L_S_SELECT TO L_R_CONNID. |
| * APPEND L_R_CONNID. |
| * Determine number of database records to be read per FETCH statement |
| * from input parameter I_MAXSIZE. If there is a one to one relation |
| * between DataSource table lines and database entries, this is trivial. |
| * In other cases, it may be impossible and some estimated value has to |
| * be determined. |
| OPEN CURSOR WITH HOLD S_CURSOR FOR |
| select vepo~venum min( vepo~matnr ) |
| from likp inner join vekp on ( likp~vbeln = vekp~vpobjkey ) |
| inner join vepo on ( likp~vbeln = vepo~vbeln ) and |
| ( vekp~venum = vepo~venum ) |
| where vepo~mandt = sy-mandt and likp~mandt = sy-mandt and vekp~mandt = sy-mandt and |
| vekp~vstel = '1100' |
| and vekp~erdat between '20130101' and '20130102' |
| group by vepo~venum. |
| ENDIF. "First data package ? |
| i_cont = 1. |
| *DO. |
| FETCH NEXT CURSOR S_CURSOR INTO (i_venum, i_matnr). |
| IF sy-subrc <> 0. |
| CLOSE CURSOR S_CURSOR. |
| RAISE NO_MORE_DATA. |
| * EXIT. |
| ENDIF. |
| *Sacamos la familia |
| select single extwg into wa_pallets-extwg |
| from mara client specified |
| where mandt = sy-mandt and matnr = i_matnr. |
| *Entrega |
| select single vbeln into wa_pallets-vbeln |
| from vepo client specified |
| where mandt = sy-mandt and venum = i_venum. |
| *Destinatario de la mercancía |
| select single kunnr into wa_pallets-kunnr |
| from likp client specified |
| where mandt = sy-mandt and vbeln = wa_pallets-vbeln. |
| *Población |
| select single ort01 into wa_pallets-ort01 |
| from kna1 client specified |
| where mandt = sy-mandt and kunnr = wa_pallets-kunnr. |
| wa_pallets-mandt = sy-mandt. |
| wa_pallets-cont = i_cont. |
| select vstel vpobjkey exidv erdat vhilm vtweg vkorg |
| from vekp client specified |
| into (wa_pallets-vstel, wa_pallets-vpobjkey, wa_pallets-exidv, wa_pallets-erdat, wa_pallets-vhilm, wa_pallets-vtweg, wa_pallets-vkorg) |
| where mandt = sy-mandt and venum = i_venum. |
| endselect. |
| append wa_pallets to E_T_DATA. |
| i_cont = i_cont + 1. |
| *ENDDO. |
| ** Fetch records into interface table. |
| ** named E_T_'Name of extract structure'. |
| * FETCH NEXT CURSOR S_CURSOR |
| * APPENDING CORRESPONDING FIELDS |
| * OF TABLE E_T_DATA |
| * PACKAGE SIZE S_S_IF-MAXSIZE. |
| * IF SY-SUBRC <> 0. |
| * CLOSE CURSOR S_CURSOR. |
| * RAISE NO_MORE_DATA. |
| * ENDIF. |
| READ TABLE e_t_data INDEX 1. |
| IF e_t_data IS INITIAL. |
| RAISE no_more_data. |
| ENDIF. |
| ENDIF. "Initialization mode or data extraction ? |
The BOLD in your code are the changes I made and it will work fine.
You just have to remove the DO condition 
Please let me know if you face any issues with this.
Thanks
Amit