Thank you, but that solutions are not for my issue. I can dial the number without problem, I can speak with the receiver using a phone terminal connected to the workcentre 6515, but I can't start the transmission once I get the fax tone from the receiver, like pressing Start button on older fax machines.
I searched the Knowledge-base and found THESE SOLUTIONS for when fax transmission fails. It doesn't exactly address the manual send issue you describe but it is worth checking out.
We use a WorkCentre 6515dn for sending and receiving faxes. Receiving works great. Sending a fax when the receiver is set on auto mode works with no problem.
The problem is we can't find how to send faxes when the receiver fax is on manual mode (i.e. when someone is answering and you ask him for the fax tone).
Please, if anyone know how to send a fax in this situation, let me know, because in those cases we must use an old fax machine and is very annoying.