Community @ The Turning Gate

I feel a real fraud asking questions about a free product.... But here goes!
I use the TTG 2014 HTML gallery plugin for all my client galleries on my site.
I use it in conjunction with some javascript I've had for ages, to add a shopping cart. It all worked fine until (I think) LR6.
Now, it appears to work OK until you actually try and order a print and instead of a filename you get 'undefined'
The same thing happens with any of the new responsive gallery templates built into LR6, so I'm guessing it's a LR problem, and not yours! (It still works fine with non-responsive layouts) I suppose I'm just trying to avoid spending $75 for the TurningGate solution, but I would love a confirmation that it's LR6 and not me......
The javascript I am using is inserted in the caption>custom text bit of Image Info. It came from someone on another forum several years back - and is no longer supported or developed as far as I can see. It is:

<script type="text/javascript"> 
var myDomain="www.yourdomain.com"; 
var imgsrc=document.getElementById("previewImage").src; 
var filename=imgsrc.replace("images/large/",""); 
filename=filename.substring(filename.lastIndexOf("/")+1,filename.length); 
var thumb=imgsrc.replace("large","thumb"); 
thumb=thumb.replace("http://" + myDomain + "/","");
thumb=thumb.replace("http://www." + myDomain + "/",""); 
returnTo=window.location.href;  </script>   
<form action="http://ww7.aitsafe.com/cf/add.cfm" method="post"> 
<input type="hidden" name="userid" value="97403082">
<input type="hidden" name="nocart"> 
<input type="hidden" name="return" value=""> 
<input type="hidden" name="product" value=""> 
<input type="hidden" name="thumb" value="">   
<script type="text/javascript"> 
document.getElementsByName("product")[0].value = filename; 
document.getElementsByName("thumb")[0].value = thumb; 
</script> 
<select size="1" name="productpr">
<option selected value="">Select size
<option value="6x4 inch :2.50">6x4 inch £2.50</option>
<option value="7x5 inch :5">7x5 inch £5.00</option>
<option value="10x8 inch :7.50">10x8 inch £7.50</option>
<option value="12x16 inch :10.00">12x16 inch £10.00</option>
</select> 
<br>
<input type="submit" name="Submit" value="Buy Photo!" 
onclick="alert('Photo has been added to your cart');" 
onkeypress="alert('Photo has been added to your cart');"> 
</form> 
<form action="http://ww7.aitsafe.com/cf/review.cfm" method="post"> 
<input type="hidden" name="userid" value="97403082">
<input type="hidden" name="return" value=""> 
<script type="text/javascript"> 
document.getElementsByName("return")[0].value =returnTo; 
document.getElementsByName("return")[1].value =returnTo; 
</script> 
<input type="submit" name="Submit" value="View Your Cart!"> 
</form> 

There's an example of a gallery here: <http://www.q-photography.co.uk/SKphotos/>

Thanks for any suggestions!

Simon