I saw the owner/group of that file was admin/admin (the user that uploaded it) but when I try to chown it to root(thinking that is the problem), it returns an "invalid user" result.
Are you su'd to root before doing the chown ??Did you check the permissions on the folder containing the chkrootkit ? Mine is /usr/local/chkrootkit-0.37
And as Gerald asked, did you cd /usr/local/chkrootkit-0.37 before running it? Jale