[OS X Emacs] Aquaemacs 2.2 Tramp - not a tramp filename

[Christoph]

Hi everybody,

I'm working with Mac OS 10.6.8 and I have installed Aquaemacs 2.2.

I want to open a remote file (or Dired Mode) via tramp and tried following 
combinations:

/User at Machine:/Fullpath to file or directory

/scp/User at Machine:/Fullpath....

I tried also /ssh/User at Machine:/Path...

I'm always geth the error " is not a tramp file".

What's wrong here?