New Post: Exception thrown and not caught

I'm receiving the following error when calling UpdateListItems using SPServices.

Message: Exception thrown and not caught
Line: 16
Char: 11590
Code: 0
URI: http:///Site%20Assets/jquery-1.6.2.min.js (this line was modified to hide our site name).

I am using SPServices 0.7.1a (min). The code is as follows (slightly redacted):

$().SPServices({
    operation: "UpdateListItems",
    async: false,
    listName: "My List",
    batchCmd: "New",
    valuepairs: [["some_x0020_field",someVariable]],
    completefunc: function(xData, Status) {
        console.log( $( xData.responseXML ) );
    },
    debug: true
});

Using Fiddler I can see the SOAP request being sent. I can confirm the list is being updated with the new record. And I see a successful response in Fiddler as well. However the completefunc code never runs and I receive the previously mentioned error.

Also, a bit of info - we just migrated our farm to new servers by:

• Installing a clean SharePoint farm
• Performing a content database restore
  

This code hasn't changed in a long time and still runs on our QA site as well as our old farm. Any thoughts?