javascriptไม่ทำงานค่ะ ช่วยดูให้หน่อยค่ะว่าติดตรงไหน

<script language="JavaScript">
			function EnableTXT()
			{
				//alert(window.document.form1.cntRow.value);
				for(var i=1;i<=window.document.form1.cntRow.value;i++)
				{
					//alert(window.document.form1.chkKPI+i);
					//alert(window.document.form1.txtTarget+i);
					
					if(document.form1.chkKPI+i.checked)
					{
						//alert(document.form1.chkKPI+i.value);
						document.form1.txtTarget+i.disabled = false;
					}
					else
					{
						//alert(document.form1.chkKPI+i.value);
						document.form1.txtTarget+i.disabled = true;
					}
				}
			}

		</script>

<tr>
																<td class="tdRight" width="25%"><b>KPIทั้งหมด :&nbsp;</b></td>
																<td class="tdLeft" width="75%">
																	<?
																			include("ConnectDB.php");
																			$ClassConDb = new MyDatabase();
	
																			mysql_query("SET character_set_results=utf8");
																			mysql_query("SET character_set_client=utf8");
																			mysql_query("SET character_set_connection=utf8");

																			$strKPIAll = "Select kpiID,kpiname from kpis";
																			$objStr = mysql_query($strKPIAll);
																			$Rows = mysql_num_rows($objStr);
																			$i = 1;
																			while($objResult = mysql_fetch_array($objStr))
																			{
																	?>
																				<input type="checkbox" name="chkKPI[]" id="chkKPI<? echo $i;?>" value="<? echo $objResult['kpiID']?>" onclick="javascript:EnableTXT();">&nbsp;<? echo $objResult['kpiname']?> &nbsp;<input type="text" name="txtTarget[]" id="txtTarget<? echo $i;?>" size="10"><br>
																				<input type="hidden" name="KPIID<? echo $i;?>" id="KPIID<? echo $i;?>"  value="<? echo $objResult['kpiID'];?>">
																	<?
																				$i += $i;
																			}
																			mysql_close();
																	?>
																		<input type='hidden' name='cntRow' value="<? echo $Rows;?>">
																<td/>
															</tr>