BusinessFault : {urn:enterprise.soap.sforce.com}InvalidSObjectFault. INVALID_TYPE: sObject type 'custom _object__c' is not supported.

we are using enterprise.wsdl and soap api to query and upsert. 

Caused by: com.oracle.bpel.client.BPELFault: faultName: {{urn:enterprise.soap.sforce.com}InvalidSObjectFault}
messageType: {{urn:enterprise.soap.sforce.com}InvalidSObjectFault}
parts: {{
fault=<sf:InvalidSObjectFault xsi:type="sf:InvalidSObjectFault" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:sf="urn:fault.enterprise.soap.sforce.com"><sf:exceptionCode>INVALID_TYPE</sf:exceptionCode><sf:exceptionMessage>sObject type 'rC_Bios__Contact_Address__c' is not supported.</sf:exceptionMessage><sf:row>-1</sf:row><sf:column>-1</sf:column></sf:InvalidSObjectFault>}cause: {null}
        at com.collaxa.cube.ws.WSInvocationManager.invoke(WSInvocationManager.java:289)