Hi Matt,
You forgot to attached the error but I think I know what the issue is, you need to delete your old templates from your portals folder.  Please take the following steps to resolve this issue:

1.  Make sure you have a full backup of your DNN install
2.  From the store admin menu, click on the page template button to go into the page template editor and delete all your page templates.
3.  In file explorer, navigate to your \portals\[portalid]\smithcart\templates folder
4.  Delete all the files in the \portals\[portalid]\smithcart\templates folder
5.  Reset iis and restart the application from the dnn host menu
6.  Go to product deletals page and see if it loads correct.

To add your CSS styles back from your old templates to your new templates you can use a dif program like "WinDif" to quickly migrate your changes into your new templates.

Let me know if you have any questions.