Ошибка при выполнении запроса Trying to store a string of length 30 into field that can only contain 20

with IBQSPRED do
  begin
    close;
    SQL.Clear;
    SQL.Add('select (case when npredu='''' then npred else npredu end) as npred from spred where kpred=:KodPred and kbank=:KodBank and nschet=:Nschet');
    ParamByName('KodPred').Value := IBQ_Zadan.FieldValues['kplat'];
    ParamByName('KodBank').Value := IBQ_Zadan.FieldValues['kmfo'];
    if trim(IBQ_Zadan.FieldValues['nschet']) = '0' then
      ParamByName('Nschet').Value := ''
    else
      ParamByName('Nschet').Value := IBQ_Zadan.FieldValues['nschet'];
      //ShowMessage(IBQ_Zadan.FieldValues['kplat']);
      //ShowMessage(IBQ_Zadan.FieldValues['kmfo']);
      //ShowMessage(IBQ_Zadan.FieldValues['nschet']);
    Open; //ERROR
    if IsEmpty then
      nplat := ''
    else
      nplat := trim(FieldByName('npred').AsString);
  end;

ParamByName('Nschet').Value := IBQ_Zadan.FieldValues['nschet'];

      ParamByName('Nschet').Value := Copy(Trim(IBQ_Zadan.FieldByName('nschet').asString),1,20);

if trim(IBQ_Zadan.FieldValues['nschet']) = '0' then
      ParamByName('Nschet').Value := ''

 ParamByName('Nschet').Value := Copy(Trim(IBQ_Zadan.FieldByName('nschet').asString),1,20);