Plesk Billing 6.x Fatal error: Unsupported operand types in..

After a totally fresh installation of Plesk Billing , as you login as a simple client you may notice an PHP Fatal error (the webpage will be blank but the errors will be visible in the log files)To fix this download (check here) the installation files of PPB version 6.0.0  and replace the following files:

AddBillingAccount.php
AddBillingAccountResponse.php
EditBillingAccount.php
EditBillingAccountResponse.php

thanx to jraidan for this , check here.