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!