Bug with Magento Extension - Customer Groups

Hi all,

I have a problem with a live Magento store. When creating an order in the admin area for a new customer, the "Customer Group" drop down has disappeared.

I need this ASAP as it is causing major problems using the admin area.

I think this has been caused by this extension:
http://www.magentocommerce.com/magento-connect/customer-group-at-registration.html

But when I disable it it still doesn't re-appear. I think this could be due to the MySQL changes the extension makes and doesn't undo when it is disabled. I have contacted the developer but he is unable to help at short notice.

I need somebody who can look at this for me

Regards