Description of Problem:

A file /usr/share/umb-scheme/prelude.scheme says, among other things,

; MAINTENANCE PROCEDURES

; (vi) -- edit this file

Ok, lets try:
==> (vi)
sh: line 1: /usr/ucb/vi: No such file or directory

Error: Edit on prelude.scheme didn't succeed; not reloading file.

Oops!  The same, of course, will happen if you will attempt
==> (edit "some.other.file")

This can be worked around if you will set EDITOR in environment but
defaults should be sane.

The same applies to releases in earlier distributions.