post the detailed error messages and/or some code? or see
XML Serialization in .NET
http://www.codeproject.com/csharp/xmlserialize.asp?print=true
Contact[] aContact = new Contact[table.Count];
table.Values.CopyTo( aContact, 0 );
// Deserialize the content of the Contact array to a XML file
XmlSerializer x = new XmlSerializer( typeof(Contact[]) );
TextWriter writer = new StreamWriter( "phonebook.xml" );
x.Serialize( writer, aContact );