The error seems to be in ac-qq1, line 209, which uses map to look at nested structures in a quasiquote.
((pair? x)
(map (lambda (x) (ac-qq1 level x env)) x))
And apparently scheme's map can't handle dotted lists.
Unfortunately I don't scheme well enough to know if another primitive does what we want... Otherwise we'll have to write a new version of map for use by quasiquote. (Or rewrite quasiquote to not use map at all, but that might be more work.)
I could do this but happen to be a little busy right now. (I wouldn't mind if someone were to beat me to it.)
I normally use "{{{" and "<<<<" as delimiteres in a plaintext . But obviously it doesn't work very well here, so I'll keep in mind to use indentation instead.