ssh to an "unkown" machine

[Mihamina Rakotomandimby]

Hi, I wanna ssh-edit a remote file.
The host is not known yet, so that I still need to accept its key.
The problem is tramp says that:
Debugger entered--Lisp error: 
(error "Cannot return from the debugger in an error")
call-interactively(find-file)
What is the problem? doesn't tramp handle the feature yet?
thank you.