I think the problem is your data. int is not a nullabe type (by default).
Try adding values to the fields that do not have values

<Contact>
	<FirstName>John</FirstName>
	<LastName>Smith</LastName>
	<Email>john.s@yahoo.com</Email>
	<FromDOW>0</FromDOW>
	<ToDOW>0</ToDOW>
	<FromHour>0</FromHour>
	<FromMinute>0</FromMinute>
	<ToHour>0</ToHour>
	<ToMinute>0</ToMinute>
	<StopSendingEmail>0</StopSendingEmail>
</Contact>