Customized Ajax Form Java Button Validation

[Organic]

We've been customizing an Ajax signup form for WHMCS: here.

 

When you choose a package, the "Next" button should unhide. It's a way of insuring the user chooses something before proceeding.

 

The problem is that the button is getting stuck in what appears to be an infinite validation loop (you can see by clicking the link above).

 

The form is just a customized version of the WHMCS Ajax Cart: here. It uses jQuery validation. Here is the code for the button:

 

{if $hiddenproduct}<input type="hidden" name="pid" value="{$pid}"/>{/if}

 

Does anyone know what the problem might be? Even a point in the right direction would be a huge help right now. Thank you!