SendFax error

[zychu]

Hi all,
When I send a fax using SendFax getting the error: "A communication failure has occured during the fax submission".
You know what the log can be found the cause of the problem? In the documentation (eg TG0061) there is nothing about the diagnosis of the application.
OTFS ver 7.0, SendFax ver 7.0.1.52
I would be grateful for any help.