Need to get a reportfrom a webinar

Hello there!
A webinar was created for a user where the registration box was checked in this webinar. So all the participants will have to register.
The user decided after a couple of weeks of people registering on the page he didn't want people to be able to register and enter the webinar directly. That was no problem for me.
Now that the user is asking for reports, he wants all the people who registered in the first two weeks to be reported. Entering the reports page, I am unable to generate a report since the option was changed.
Is it possible to recover the registered users?
Thanks for the help.