Event end time changing

Hi,

I use CRM to set up appointments (Events) with clients and then update information after the appointment. The appointments can be of varying times and up until recently it has worked well.

However, now when I edit the appointment afterwards the date shows a clash of events and changed the end time to half an hour after after the start time. How can I go back to having no notifications of clashed of events and have the set end time stay the same?

Thanks
Tracey