Synchronisation completed with 1 errors

A small window pops on my screen everyday with an error saying "Synchronisation completed with 1 errors."

When I view the error in details, here is what I got:

The SSL connection could not be established, see inner exception.

Action: ReceiveCalendar

Calendar: Children

I import google calendar and "Children" is one of the categories in my google calendar.

I don't know what to do next. Please guide. Thanks!