In our marketing cloud platform, we have synchronized salesforce contact object into Synchronized Data Extensions folder. Now I wanna retrieve the object named 'Contact_Salesforce_1' by SOAP api, but I got the following error response:

    <RetrieveResponseMsg xmlns="http://exacttarget.com/wsdl/partnerAPI">
         <OverallStatus>Error: Invalid object name 'C100015214.Contact_Salesforce_1'.</OverallStatus>
         <RequestID>1464e09d-3020-4444-838c-f0c3b3d65630</RequestID>
    </RetrieveResponseMsg>

My request is:

       <RetrieveRequestMsg xmlns="http://exacttarget.com/wsdl/partnerAPI">
    	  <RetrieveRequest>
    		 <ObjectType>DataExtensionObject[Contact_Salesforce_1]</ObjectType>
    		 <Properties>Name</Properties>
    	  </RetrieveRequest>
       </RetrieveRequestMsg>

Who can tell me why the error occured?
Thanks a lot!