function check_form() {
  var error_message = "Wystąpiły błędy w trakcie przetwarzania formularza!\n\n";
  var error_found = false;
  var error_field;
  var keywords = document.advanced_search.keywords.value;
  var dfrom = document.advanced_search.dfrom.value;
  var dto = document.advanced_search.dto.value;
  var pfrom = document.advanced_search.pfrom.value;
  var pto = document.advanced_search.pto.value;
  var pfrom_float;
  var pto_float;

  if ( ((keywords == '') || (keywords.length < 1)) && ((dfrom == '') || (dfrom == 'dd/mm/yyyy') || (dfrom.length < 1)) && ((dto == '') || (dto == 'dd/mm/yyyy') || (dto.length < 1)) && ((pfrom == '') || (pfrom.length < 1)) && ((pto == '') || (pto.length < 1)) ) {
    error_message = error_message + "* Przynajmniej jedno z pól w formularzu wyszukiwania musi być podane.\n";
    error_field = document.advanced_search.keywords;
    error_found = true;
  }

  if ((dfrom.length > 0) && (dfrom != 'dd/mm/yyyy')) {
    if (!IsValidDate(dfrom, 'dd/mm/yyyy')) {
      error_message = error_message + "* Błędna Data Od.\n";
      error_field = document.advanced_search.dfrom;
      error_found = true;
    }
  }

  if ((dto.length > 0) && (dto != 'dd/mm/yyyy')) {
    if (!IsValidDate(dto, 'dd/mm/yyyy')) {
      error_message = error_message + "* Błędna Data Do.\n";
      error_field = document.advanced_search.dto;
      error_found = true;
    }
  }

  if ((dfrom.length > 0) && (dfrom != 'dd/mm/yyyy') && (IsValidDate(dfrom, 'dd/mm/yyyy')) && (dto.length > 0) && (dto != 'dd/mm/yyyy') && (IsValidDate(dto, 'dd/mm/yyyy'))) {
    if (!CheckDateRange(document.advanced_search.dfrom, document.advanced_search.dto)) {
      error_message = error_message + "* Data Do musi być większa lub równa Dacie Od.\n";
      error_field = document.advanced_search.dto;
      error_found = true;
    }
  }

  if (pfrom.length > 0) {
    pfrom_float = parseFloat(pfrom);
    if (isNaN(pfrom_float)) {
      error_message = error_message + "* Cena Od musi być liczbą.\n";
      error_field = document.advanced_search.pfrom;
      error_found = true;
    }
  } else {
    pfrom_float = 0;
  }

  if (pto.length > 0) {
    pto_float = parseFloat(pto);
    if (isNaN(pto_float)) {
      error_message = error_message + "* Cena Do musi być liczbą.\n";
      error_field = document.advanced_search.pto;
      error_found = true;
    }
  } else {
    pto_float = 0;
  }

  if ( (pfrom.length > 0) && (pto.length > 0) ) {
    if ( (!isNaN(pfrom_float)) && (!isNaN(pto_float)) && (pto_float < pfrom_float) ) {
      error_message = error_message + "* Cena Od musi być większa lub równa Cenie Do.\n";
      error_field = document.advanced_search.pto;
      error_found = true;
    }
  }

  if (error_found == true) {
    alert(error_message);
    error_field.focus();
    return false;
  } else {
    RemoveFormatString(document.advanced_search.dfrom, "dd/mm/yyyy");
    RemoveFormatString(document.advanced_search.dto, "dd/mm/yyyy");
    return true;
  }
}

function popupWindow(url) {
  window.open(url,'popupWindow','toolbar=no,location=no,directories=no,status=no,menubar=no,scrollbars=yes,resizable=yes,copyhistory=no,width=450,height=280,screenX=150,screenY=150,top=150,left=150')
}