When attempting to set the node value in an InfoPath form with code, “schema validation” errors may appear.   This is primarily caused by attempting to set the value of a field with one of the following data types:

• Whole Number (integer)
• Decimal (double)
• Date (date)
• Time (time)
• Date and Time (dateTime)

The workaround is to remove the “nil” attribute from the element:

public void DeleteNil(XPathNavigator node)
{
if (node.MoveToAttribute(“nil”, “http://www.w3.org/2001/XMLSchema-instance”))
      node.DeleteSelf();
}

Additional Resources:

•  https://blogs.msdn.microsoft.com/infopath/2006/11/28/the-xsinil-attribute/