Just noticed the following error log in Console:
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11/16/13 9:45:33.186 PM CalendarAgent[215]: [com.apple.calendar.store.log.exchange.queue] [Save failed in -[CalOperationQueue executeOperations]. Error = Error Domain=NSCocoaErrorDomain Code=1560 "Multiple validation errors occurred." UserInfo=0x7fcfe0c78e10 {NSDetailedErrors=(
"Error Domain=CalCalendarStorePersistenceErrorDomain Code=1550 \"Alerts that open files or scripts must include a file path.\" UserInfo={\n CalAlarmUID = \"44F739FB-6617-4400-87C5-0545D0F1153A\";\n CalCalendarItemUID = \"598680C1-E4C1-4269-920B-85D4D4F4D52F\";\n CalCalendarUID = \"D7FCEC40-B0B0-4AF8-B6B1-0D326854CA9A\";\n CalManagedObjectType = CalManagedAlarm;\n NSLocalizedDescription = \"Alerts that open files or scripts must include a file path.\";\n}",
"Error Domain=CalCalendarStorePersistenceErrorDomain Code=1550 \"Alerts that open files or scripts must include a file path.\" UserInfo={\n CalAlarmUID = \"8DBF3C93-E323-4851-9282-B3BFD4B7F251\";\n CalCalendarItemUID = \"598680C1-E4C1-4269-920B-85D4D4F4D52F\";\n CalCalendarUID = \"D7FCEC40-B0B0-4AF8-B6B1-0D326854CA9A\";\n CalManagedObjectType = CalManagedAlarm;\n NSLocalizedDescription = \"Alerts that open files or scripts must include a file path.\";\n}"
)}. {
NSDetailedErrors = (
"Error Domain=CalCalendarStorePersistenceErrorDomain Code=1550 \"Alerts that open files or scripts must include a file path.\" UserInfo={\n CalAlarmUID = \"44F739FB-6617-4400-87C5-0545D0F1153A\";\n CalCalendarItemUID = \"598680C1-E4C1-4269-920B-85D4D4F4D52F\";\n CalCalendarUID = \"D7FCEC40-B0B0-4AF8-B6B1-0D326854CA9A\";\n CalManagedObjectType = CalManagedAlarm;\n NSLocalizedDescription = \"Alerts that open files or scripts must include a file path.\";\n}",
"Error Domain=CalCalendarStorePersistenceErrorDomain Code=1550 \"Alerts that open files or scripts must include a file path.\" UserInfo={\n CalAlarmUID = \"8DBF3C93-E323-4851-9282-B3BFD4B7F251\";\n CalCalendarItemUID = \"598680C1-E4C1-4269-920B-85D4D4F4D52F\";\n CalCalendarUID = \"D7FCEC40-B0B0-4AF8-B6B1-0D326854CA9A\";\n CalManagedObjectType = CalManagedAlarm;\n NSLocalizedDescription = \"Alerts that open files or scripts must include a file path.\";\n}"
);
}]