JQuery Ajax Post sometimes works - php

Question

I have an issue with JQuery and Ajax. Sometimes my code works just fine, sometimes it just will not. Other times I need to press a down arrow once in order to make the up arrows work, which is strange enough...
In IE or in Firefox, the lack of response happens more rarely than it does in Chrome.
The website in question is here:
http://www.dungeoncrawler.com/kickstarter_2013/calculator/
If you need to login, try:
ID: webmaster#geoste.ca
Pass: 123456789
Here is an example of my code:
Javascript JQuery function : first either chnQuantUp or chnQuantDn is called, and then the data gets passed to doCrtUpd which does the actual JQuery call.
function doCrtUpd(crtID,itmAmt,itmStrID)
{
// Call AJAX to update cart quantities
if (crtID)
{
$.ajax({
type: 'POST',
url: 'inc-kspldgman.php',
data: {cartordrnum: crtID,itmamt: itmAmt,storeitmkey: itmStrID, doaction: "UPDITM"},
async: true,
success: function (d)
{
reLoadDivs();
},
error: function (d)
{
alert(d);
}
});
}
}
function chnQuantUp(frmEle,frmEleID,crtID,itmStrID)
{
tmpvar2 = frmEle + frmEleID;
tmpvar1 = eval("document.frmStrItms."+ tmpvar2 +".value");
if (isNaN(tmpvar1))
{
tmpvar1 = 1;
}
else
{
tmpvar1 = parseInt(tmpvar1);
tmpvar1++;
}
eval("document.frmStrItms."+ tmpvar2 +".value = " + tmpvar1);
doCrtUpd(crtID,tmpvar1,itmStrID);
}
function chnQuantDn(frmEle,frmEleID,crtID,itmStrID)
{
tmpvar2 = frmEle + frmEleID;
tmpvar1 = eval("document.frmStrItms."+ tmpvar2 +".value");
if (isNaN(tmpvar1))
{
tmpvar1 = 0;
}
else
{
tmpvar1 = parseInt(tmpvar1);
}
tmpvar1--;
if (tmpvar1 < 0)
{
tmpvar1 = 0;
}
eval("document.frmStrItms."+ tmpvar2 +".value = " + tmpvar1);
doCrtUpd(crtID,tmpvar1,itmStrID);
}
Example of my HTML, one of the store items:
<div name="frmEle14" id="frmEle14" class="item" style=" background-image: url(./gallery/calc_ID_84.png);">
<div class="item_name">GREENKNEE, PPM</div>
<div class="item_count_5">
<div align="center">
<img src="images/calc_arrow_up_lw.jpg" border="0" class="arrow_btn1" /><br />
<input type="text" name="frmeleamt14" id="frmeleamt14" class="count_box" value="0" size="3" maxlength="3" onkeyup="javascript:doManChng('0',document.frmStrItms.frmeleamt14.value,'38','frmeleamt14');" /><br />
<input type="hidden" name="frmelesku14" id="frmelesku14" value="GVN-DCM-0005-CHAMP-PPM" />
<input type="hidden" name="frmelesalecode14" id="frmelesalecode14" value="NONE" />
<input type="hidden" name="frmeleitmkey14" id="frmeleitmkey14" value="38" />
<input type="hidden" name="frmgvnlinekey14" id="frmgvnlinekey14" value="0" />
<img src="images/calc_arrow_down_lw.jpg" border="0" class="arrow_btn2" />
<input type="hidden" name="frmelepicnme14" id="frmelepicnme14" value="calc_ID_84.png" />
</div>
</div>
<div class="item_price">$3.00</div>
</div>
And the PHP code that handles the actual addition to the database:
if ($cartordrnum)
{
// Start UPDATE
if ($doaction == "UPDITM")
{
$rspns = "";
// Get store item's data that we need, such as price per unit
$sql = "SELECT item_unitprice,salecode FROM store_items WHERE itemkey = ".$storeitmkey.";";
$getitmdata1 = mysqli_query($conn,$sql);
$getitmdata = mysqli_fetch_array($getitmdata1);
$itemunitprice = $getitmdata['item_unitprice'];
settype($itemunitprice,"float");
$salecode = $getitmdata['salecode'];
settype($salecode,"string");
$getitmdata = null;
$getitmdata1 = null;
// Do new item total if it has not already been calculated via salecode
if ($itmttl == 0)
{
$itmttl = ($itmamt * $itemunitprice);
}
$gvnlinekey = 0;
$dbitmamt = 0;
$sql = "SELECT lineitmkey, linequant FROM gvn_lineitems WHERE storeitmkey = ".$storeitmkey." AND code_note IS NULL ORDER BY lineitmkey DESC LIMIT 0,1;";
$chklineitm1 = mysqli_query($conn,$sql);
if (mysqli_num_rows($chklineitm1))
{
$chklineitm = mysqli_fetch_array($chklineitm1);
$gvnlinekey = $chklineitm['lineitmkey'];
settype($gvnlinekey,"integer");
$dbitmamt = $chklineitm['linequant'];
settype($dbitmamt,"integer");
}
$chklineitm = null;
if ($gvnlinekey)
{
if ($itmamt)
{
// Check if amounts have changed.
if ($dbitmamt != $itmamt)
{
// We have a change, so do an update.
// Do DB update
$sql = "UPDATE gvn_lineitems SET linequant = ".$itmamt.", linesubttl = ".$itmttl.", linettl = ".$itmttl." WHERE lineitmkey = ".$gvnlinekey.";";
if (mysqli_query($conn,$sql))
{
$rspns = "UPDATED";
}
}
}
else
{
// Delete the lineitem because it has a zero or negative amount
$sql = "DELETE FROM gvn_lineitems WHERE lineitmkey = ".$gvnlinekey." AND code_note IS NULL;";
if (!mysqli_query($conn,$sql))
{
$rspns = "DELETED1";
}
}
}
else
{
// Insert new line item
if ($itmamt > 0)
{
$sql = "INSERT INTO gvn_lineitems (ordrnumkey,storeitmkey,linequant,linesubttl,linettl) VALUES (".$cartordrnum.",".$storeitmkey.",".$itmamt.",".$itmttl.",".$itmttl.");";
if (mysqli_query($conn,$sql))
{
$rspns = "ADDED";
}
}
else
{
// Delete the lineitem because it has a zero or negative amount
$sql = "DELETE FROM gvn_lineitems WHERE storeitmkey = ".$storeitmkey." AND code_note IS NULL;";
if(mysqli_query($conn,$sql))
{
$rspns = "DELETED2";
}
}
}
$chklineitm1 = null;
//echo $rspns;
}