Remote branch can not be resolved as commit?

[Kendall Shaw <kshaw@kendallshaw.com>]

I am trying to setup a repository for use inside the LAN, but I have 
been unable to checkout any branch so far. I am very new to git.

The repository is being served from gitblit over https. I have 
GIT_SSL_NO_VERIFY=true. The repository was created from git svn.

git ls-remote

shows the remote branches, e.g.:

... refs/remotes/2.0.3
... refs/remotes/trunk

git branch -r

shows none of the remote branches.

git checkout -b new-2.0.3 origin/2.0.3

produces:

fatal: git checkout: updating paths is incompatible with switching branches.
Did you intend to checkout 'origin/2.0.3' which can not be resolved as 
commit?

What does that mean?

I get the same result after each of these:

git fetch

git remote update
git fetch

git add remote stage-repo https://example.com:8443/git/blah-tools.git
git fetch stage-repo
git checkout -b new-2.0.3 stage-repo/2.0.3

Can you explain what the error message means, and what I am doing wrong?

Kendall