emacs: Terminal type "..." is not powerful enough to run Emacs.

This message can occur for one of two reasons:

Your terminal type may be set incorrectly. Type "ttyset" and enter your terminal type. See here for more details.
You're probably on a terminal that can't move the cursor around, such as a DECwriter. Emacs will only work on screen-oriented terminals. If you are using a screen-oriented terminal, the terminal type is probably set wrong and you should use the "ttyset" command to reset it.