SAP 6.5 Can not find RFC

Hi All
Now I face this issue when upgrade SAP4.6 to SAP6.5.
Message [SAP.105.9205] WmSAP Adapter: Function interface named “BAPI_BILLINGDOC_CREATE” does not exist on SAP system with system id “CQA”.

The RFC works well on SAP4.6. But when I create the RFC adapter on SAP6.5, I can search the function name, but can not see any input/ouput parameters.
Does someone know what is the problem? It is webMethods issue or SAP system configuration problem?

Below is our server information:
IS version
SAP version 6.5
OS Platform IA64W
OS Version B.11.23
Current User root
Java Data Model 64-bit
Java Version (49.0)