BAPI Return Message Clarification needed...

I am integrating Lotus Notes with SAP.  I execute a BAPI,
BAPI_CUSTOMER_CHECKEXISTENCE, and it returns the message: "User does not
exist in master record".  However, I can see the customer record in the
KNA1 master data table.  I am making the BAPI call from Notes.  Can anyone
shed light on the return message and why it cannot find the customer in the
table?

Thanks,
Sean

Sean D. Burnett
Lotus Notes Developer
Fleetwood Retail Corp.