I have tried this in 2.88 and 2.90 with identical results. I want to require my customers to log in to DNN before they buy something. In the Settings area:

Confirmation Page Configuration

Hide login and password – checked

In the Product set screen, i have Require login checked.

If I logout of DNN, then place an order, I am offered the Create an Account / Sign In to Your Account screen. I fill in the If you do not have an account side, then continue the checkout process. On completion of the final step (the Submit Order button), I get the following, just above the BuyNow module:

A critical error has occurred.

Object reference not set to an instance of an object.

If I first log into DNN as a valid existing user, I can complete the order process perfectly. If I fill in the Sign In To Your Account side instead of the Create an Account side, then everything works perfectly.

So -- what exactly are the settings I need? I want customers to log in to DNN -- or create a new DNN login if they are newcomers -- before they buy something.

If I clear the General Cart Configuration / Show Login Screen checkbox, and clear the Confirmation Page Configuration / Hide Login and Password checkbox, then it works. As others have commented in different threads, there are two confusing things about this:

1. The "Please only click the Submit Order button once" is confusing, because if the un-logged-in user clicks the Submit Order button before filling in the Login Information panel, the screen refreshes with *Required tags beside the empty boxes (Login, Password, Confirm Password). The fix for this would be easy. If the user has not logged in, hide the Submit Order button and make the screen look something like this:

To complete your order, you must be a registered user of this site. Registration is free and easy:

When the user successfully registers (or logs in), then clear the login stuff and display the Submit Order button and its "conly click once" warning.