Error while executing Check Out Service in UCM

Hi,

We are trying to execute ucm CHECKOUT_SUB service using java code but we are getting below error.

Error:

Event generated by user 'weblogic' at host 'indelgicho04:16200'. Unable to check out 'INDELGICHO0416015421'. A previous version of the content item has been referred to incorrectly. 

We are passing 'CHECKOUT_SUB' as parameter in the service definition of our custom service and getting it as parameter in java.

//service definition

<td>CONVERT_DOC_FILE_TO_PDF</td>

  <td>DocService

  0

  MSG_PAGE

  null

  null<br>

  null</td>

  <td>3:convertFileToPdf:CHECKOUT_SUB,CHECKIN_SEL::null</td>

//java

m_binder.putLocal("dID", "2177");