I am randomly (at least it seems so) getting this exception. I will fill more info as I find it. I may download the source to debug further.
I have traced down the exception to the vCalendar plugin. claws-mail.exe [5148] Unhandled exception at 0x6fa01aa6 in claws-mail.exe: 0xC0000005: Access violation reading location 0x0000001c. call stack vcalendar.dll!6fa01aa6()