Greetings,
First create a test repository with two commits:
mkdir gittest3 cd gittest3 git init echo foo > foo git add foo git commit -m "Foo" echo foo >> foo git add foo git commit -m "2nd. foo"
Now start gitk, point at the first commit and from the context menu select "Reset master branch to here" and then "Hard:...".
The result is 'can not find channel named "1"'.
git reset --hard HEAD\^1 in the same repository works fine.
Tested with 159c88e5ae95c5b02298193c1658fac5919c8012 (1.6.1 plus a few commits) on Windows XP.
-- Hannu