looks like you hand edited the code to add the forth column in rather than use the Update record interface.
change lines 79 - 81:
$WA_fieldValuesStr = "".((isset($_POST["Artikel1"]))?$_POST["Artikel1"]:"") ."" . "|" . "".((isset($_POST["Artikel2"]))?$_POST["Artikel2"]:"") ."" . "|" . "".((isset($_POST["Artikel3"]))?$_POST["Artikel3"]:"") ."|" . "".((isset($_POST["Artikel4"]))?$_POST["Artikel4"]:"") ."";
$WA_columnTypesStr = "none,none,NULL|none,none,NULL|none,none,NULL";
$WA_comparisonStr = "=|=|=";
to:
$WA_fieldValuesStr = "".((isset($_POST["Artikel1"]))?$_POST["Artikel1"]:"") ."" . "|" . "".((isset($_POST["Artikel2"]))?$_POST["Artikel2"]:"") ."" . "|" . "".((isset($_POST["Artikel3"]))?$_POST["Artikel3"]:"") ."" . "|" . "".((isset($_POST["Artikel4"]))?$_POST["Artikel4"]:"") ."";
$WA_columnTypesStr = "none,none,NULL|none,none,NULL|none,none,NULL|none,none,NULL";
$WA_comparisonStr = "=|=|=|=";