I saw another ticket on this (https://www.joomlart.com/forums/d/24425-registrations-fail-error-about-invalid-field-user-account-exists-with-email), but it was closed because it could not be replicated by support.
I'm getting this error as well - DT Register 4.2.4.
I upgraded the site because the client was having trouble getting Simple Group Registration to display correctly. I'm not sure of the chain of events, but it was originally set up as Detailed Group Registration, but was showing this:
It seems that upgrading to DT Register 4.2.4 fixed that error, but now I'm getting the subject error when registering for an event without being logged in:
I have the setting for the event - "Joomla User Auto-Creation" set to "No". Yet the above error appears. I changed the setting to "Yes (optional)" and tried again - but it returns the same error - REQUIRING me to log in!
This function is broken - it breaks sites, just as the other person reported.
You have the credentials for this website - log in and check the email address I used to create your account and try registering for the golf event using that email address. You will see the error for yourself.
Also, a reminder: there has been an issue for quite some time that prohibits group registrations from using the same email address for each member of the group. As it is often an administrative assistant who registers groups for events for their bosses, they prefer to be the email addressee for all confirmations and communications. When they get this error, they sometimes enter fake email addresses to get past it - this creates problems for our Mailchimp integration and other export uses of the data.
Thank you,
Ernie