Checkboxes not selectable. Plugin: Easy Registration Forms

I added this plug in to my website for people to sign up for an event.

Now I wanted to create check boxes, in order for people to select on which date they want to attend (3 days possible).

I tried it with the “select” drop down. But for some reason I can’t select multiple options even though I activated the ” multiple selections”.

Then I tried it with the “Checkbox Group”, which i would prefer in style. But there i could not select even one. It was just a checkbox as layout but i could not select anything.

Please advise how i can solve this problem.

Thank you

Rebecca