Hi Axel,
I dont know if you solved your problem, but I had the same problem and solved it.
In the trx LPD_CUST, you have the System Alias SAP_ECC_FINANCIALS. You must create a RFC Destination with this name, of the H type and with this URL: <server_domain>:<port> and very important, with this prefix /sap/bc/ui2/nwbc/, and ready.
Regards,
Johnny,