This is a problem of dates in one or more events.
Do you have a link, so that i can check it, and give your the events with a problem ?
Remember that Joomla recommends to never activate error reporting on an online website. This is for developper, or debugging a site.
A bug was introduced in the first releases of iCagenda v3.
So, this may not be a just added event causing trouble.
In the next release, i will add the first step of the new dates system i'm working on, and so, it won't be possible to save an event if dates aren't okay
