Serialization Assigning Value to Properties getting Error

I converted some XSD to C# Classes where are Link with Each Other also they have Properties with Return Type but when i create an Object or a class and Assign A Value to Property its Give me an Error

 

Cannot implicitly convert type 'int' to 'class name' also Covert Class is Not Working

 

ObjectEnvelope objectEnvelope = new ObjectEnvelope();

objectEnvelope.DocumentReference.DocumentID = 4;

 

Cannot implicitly convert type 'int' to 'Namespcae and class Name'