I\'ve had problems with autotest before which I resolved by downgrading from ZenTest 4.1.4 to 4.1.3.
$ ruby -v ruby 1.8.7 (2008-08-11 patchlevel 72) [univers
I had a similar problem which I resolved by downgrading to 4.0.0. Unfortunately I didn't have time to investigate why this happened in the first place, but I would be interested to know.