[41stNocker]

Вопрос снят.
Проблему решил так:

Код:

var
items: IHTMLElementCollection;
b:boolean;
begin
  field := theForm.Item(fieldName,instance) as IHTMLElement;
  if Assigned(field) then
    if field.tagName = 'INPUT' then
    begin
      inputField := field as IHTMLInputElement;
      if inputField.type_='hidden' then begin
        items:=(fromForm.tags('INPUT') as IHTMLElementCollection);
        b:=false;
        for i:=0 to items.length-1 do
         if (items.item(i,0) as IHTMLInputElement).name=fieldName then
          if b then begin
                      inputField:=(items.item(i,0) as IHTMLInputElement);
                      break
                    end
               else b:=true;
      end;
    end;
(...)