Runtime error in My Query

Question

HI!
I created a abap query and added few additional fields with codes in them and tried running the query. When I run teh query with selections on my selection screen it runs well and gives me output correctly but when I run it open without any selection I geta  runtime error with following description.
Short text
    Field symbol has not yet been assigned.
__What happened?__    Error in the ABAP Application Program
    The current ABAP program "AQZZZSD=========ZSD_LISTOFFLST" had to be terminat
     because it has
    come across a statement that unfortunately cannot be executed.
Error analysis    You attempted to access an unassigned field symbol
    (data segment 27).
    This error may occur if
    - You address a typed field symbol before it has been set with
      ASSIGN
    - You address a field symbol that pointed to the line of an
      internal table that was deleted
    - You address a field symbol that was previously reset using
      UNASSIGN or that pointed to a local field that no
      longer exists
    - You address a global function interface, although the
      respective function module is not active - that is, is
      not in the list of active calls. The list of active calls
      can be taken from this short dump.
How to correct the error
    If the error occures in a non-modified SAP program, you may be able to
    find an interim solution in an SAP Note.
    If you have access to SAP Notes, carry out a search with the following
    keywords:
    "GETWA_NOT_ASSIGNED" " "
I am not sure why its running ok when I provide selection and it gives error when I ran it open.
Thanks

Answer 1

The code where it shows error :
loop at gt_konv assigning <fs_konv>
   where kposn = vbrp-posnr
     and ( kschl = 'ZPRL' or kschl = 'ZWRO' or
           kschl = 'ZSPT' or kschl = 'ZWSU' or
           kschl = 'ZOTH' or kschl = 'ZQUA' or
           kschl = 'ZTAR' or kschl = 'ZCMD' ).
    add <fs_konv>-kwert to unitpr.
  endloop.
  unitpr = ( unitpr / vbrp-fkimg ).
  uomup = <fs_konv>-kmein.
  If lines( gt_konv ) gt 0.<<<<<<<<,<<<<<<<Runtime error point is here
  clear psagediff.
  IF ( PRICEDIFF <> '0.00' AND  LPRICE <> '0.00' ).
    PSAGEDIFF = ( PRICEDIFF / LPRICE ) * 100.
    else.
     PSAGEDIFF = '0.00'.
     endif.
     endif.
* Logic in code section
  case v_pricetype.
    when '00'.
      pricetype = 'Others'.
    when '01'.
      pricetype = 'List'.
    when '02'.
      pricetype = 'Off-List'.
    when '03'.
      pricetype = 'No Price'.
  endcase.