Group registration not working anymore

We have used Event Booking fot the last 3 years to sell courses.
Now, we just recently discovered that on SOME courses Group registration doesn't work anymore.
Single registration works, and group registration works on other courses...but not on some courses

see: www.pipeline.it/it/4393-moc-20761-queryi...ct-sql/view_edizioni
try to register more than 1 people, fill the details for the first registrant, and you cannot proceed...

There might be something changed on your site causing the issue. What Joomla version and Events Booking version you are using (must be very old version)

Could you afford to update your site to latest version of Events Booking and check it again?

If not, then please submit a support ticket sending us super admin account of your site and the link to the page which doesn't work so that we can check it (although if you purchased the product from 3 years ago, your support time had expired)

Regards,

Tuan