[TYPO3-project-seminars] Fatal error when unregistering because of a undefined function - solution?

[Gregory Blaser]

Hello all

I'm using seminars 0.7.0 and Typo 4.2.3 for a customer project, currently 
we're implementing the seminar manager in the website.

While testing the software we experienced the following error:
Fatal Error: Call to undefined method 
tx_seminars_registrationBagBuilder::limitToSeatsEqualOrLessThanVacancies() 
in 
/home/www/web487/html/typo3conf/ext/seminars/class.tx_seminars_registrationmanager.php 
on line 620

This happens when we try to unregister from an event from the "My 
Events"¨-view.

Can you help me out? We don't know what to do, it seems that the function 
isn't defined.

Thanks in advance!

Best Regards,
Greg