Vat Tax ID is one of our extensions. Please open a support ticket with us, there is a link in your extension and on the support tab on the MarketPlace extension page
http://marketplace.abantecart.com/index.php?rt=product/vendor_product/support&product_id=325contacting the extension developer is the best way to get good support for an extension. You should also provide as much info as possible - what cart verision is enabled, any other extensions that you have installed, any template other than the core template. All these things help to solve your issue.
Our extensions are developed and tested to work with unmodified default AbanteCart installations. We also insure that all of our extensions work with each other without conflict.
File Modifications: If you require support and have modified any files or have other extensions (non-WHY2), please tell us about these, we will do our best to solve your issues to use our extensions or instruct you in the necessary changes that need to be made. But our responsibility is limited to best effort.
The Support TeamWe Hear You 2, Inc. (WHY2)