System Error: Missing entity type information. sObject requires a separate 'type' field be sent

[AshuShri]

I am receiving an error while calling upsert method to import the data into Salesforce.

"Missing entity type information. sObject requires a separate 'type' field be sent."

I have checked that value for 'type' has been set before calling upsert method

Code snippet  of sobject class -

[XmlType(Namespace="urn:sobject.partner.soap.sforce.com")]

public class sObject

{

[

XmlAnyElement]

publicXmlElement[] Any;

[

XmlElement("fieldsToNull", IsNullable=true)]

publicstring[] fieldsToNull;

[

XmlElement(IsNullable=true)]

publicstringId;

publicstringtype;

}

Any suggestion would be helpful.