Problem with git + DiffMerge on OS X

I have configured Sourcegear DiffMerge to be my default git merge tool using the following instructions:

git config --global diff.tool diffmerge
git config --global difftool.diffmerge.cmd "diffmerge \"\$LOCAL\" \"\$REMOTE\""

git config --global merge.tool diffmerge
git config --global mergetool.diffmerge.cmd "diffmerge --merge --result=\"\$MERGED\"
\"\$LOCAL\" \"\$BASE\" \"\$REMOTE\""
git config --global mergetool.diffmerge.trustexitcode false

Source: http://www.andrejkoelewijn.com/wp/2010/01/08/configure-diffmerge-with-git/

However when I run git mergetool I get the following error:

What could be the cause of this issue?