Usually the acroread executable is the one you mentioned in your first post: /usr/local/Adobe/Acrobat7.0/bin/acroread. Under the directory /usr/bin you have a link to the executable, since /usr/bin is usually in every user's path:
$ ls -l /usr/bin/acroread
lrwxrwxrwx 1 root root 40 Oct 13 09:53 /usr/bin/acroread -> /usr/local/Adobe/Acrobat7.0/bin/acroread
Anyway, for some reason you have another link or executable under the /sbin directory, which is named acroread. This will be executed, due to the fact that /sbin is the first encountered in the PATH environment variable, before /usr/bin. Indeed the shell looks for commands in the directories specified in $PATH following the same order: the first executable encountered is the one actually executed.
In short, you have to find out where /sbin/acroread comes from, what is it and eventually delete it. Or create an alias to force the execution of /usr/bin/acroread: