Git checkout: updating paths is incompatible with switching branches

First, clone a remote Git repository and cd into it:

$ git clone git://example.com/myproject
$ cd myproject

Next, look at the local branches in your repository:

$ git branch
* master

But there are other branches hiding in your repository! You can see these using the -a flag:

$ git branch -a
* master
  remotes/origin/HEAD
  remotes/origin/master
  remotes/origin/v1.0-stable
  remotes/origin/experimental

If you just want to take a quick peek at an upstream branch, you can check it out directly:

$ git checkout origin/experimental

But if you want to work on that branch, you'll need to create a local tracking branch which is done automatically by:

$ git checkout experimental

and you will see

Branch experimental set up to track remote branch experimental from origin.
Switched to a new branch 'experimental'

Here, "new branch" simply means that the branch is taken from the index and created locally for you. As the previous line tells you, the branch is being set up to track the remote branch, which usually means the origin/branch_name branch.

Now, if you look at your local branches, this is what you'll see:

$ git branch
* experimental
  master

You can actually track more than one remote repository using git remote.

$ git remote add win32 git://example.com/users/joe/myproject-win32-port
$ git branch -a
* master
  remotes/origin/HEAD
  remotes/origin/master
  remotes/origin/v1.0-stable
  remotes/origin/experimental
  remotes/win32/master
  remotes/win32/new-widgets

At this point, things are getting pretty crazy, so run gitk to see what's going on:

$ gitk --all &

The easiest way would be to find the head commit of the branch as it was immediately before the rebase started in the reflog...

git reflog

and to reset the current branch to it (with the usual caveats about being absolutely sure before reseting with the --hard option).

Suppose the old commit was HEAD@{2} in the ref log:

git reset --hard HEAD@{2}

In Windows, you may need to quote the reference:

git reset --hard "HEAD@{2}"

You can check the history of the candidate old head by just doing a git log HEAD@{2} (Windows: git log "HEAD@{2}").

If you've not disabled per branch reflogs you should be able to simply do git reflog branchname@{1} as a rebase detaches the branch head before reattaching to the final head. I would double check this, though as I haven't verified this recently.

Per default, all reflogs are activated for non-bare repositories:

[core]
    logAllRefUpdates = true