I get this error after I created a class from my xsd file using the xsd.exe tool. So I searched the net and found a solution. Here is the link: http://satov.blogspot.com/200
For my case, the issue cases due to an invalid declaration for XmlArrayItem property attribute.
From
[XmlArrayItem("MyArray", typeof(string))]
public List<ClassName> Items{ get; set; }
I changed with appropriate type: from string to ClassName
[XmlArrayItem("MyArray", typeof(ClassName))]
public List<ClassName> Items{ get; set; }
Hope this helps!