In Version 3.6.4 of the NewtekCart, there is a bug where a combination of free shipping and using OPC will not allow the user to check out.
Click here to download One-page-checkout.zip
Example path to the folder:
Typically you will only have flat and original as your skin folders, but if you built your own or installed one of our custom skins you may have more. Make sure this file makes it into those as well.
If after uploading this file it does not work right away, try force refreshing your browser using the command Ctrl + F5.
If you have any questions, please technical support at firstname.lastname@example.org.