service order-Error during account assignment

HI experts,

I am facing a problem in CRM when saving Service Orders.

Issue:No account assignment found for this service process

An error has occurred in the system XXX while copying the document

Message no. CRM_ORDER_MISC 020

Diagnosis

Errors occurred while transferring the document into another system.To view the error messages,see the enclosed log.

Transmission log

No account assignment found for this service process (Notification E CRM_SRV_LOG_EXT_OLTP 008)

Actually,We have a problem about service order,how to integration with WBS element.

We can see Account assignment in service order item from GUI,but search help is nothing.

Account assignment is missing in UI.

If anyone know it,please share with me.

Thank you.