Found a swap file by the name

Looks like you have an open git commit or git merge going on, and an editor is still open editing the commit message.

Two choices:

1. Find the session and finish it (preferable).
2. Delete the .swp file (if you're sure the other git session has gone away).

Clarification from comments:

• The session is the editing session.
• You can see what .swp is being used by entering the command :sw within the editing session, but generally it's a hidden file in the same directory as the file you are using, with a .swp file suffix (i.e. ~/myfile.txt would be ~/.myfile.txt.swp).

Accepted answer fails to mention how to delete the .swp file.

Hit "D" when the prompt comes up and it will remove it.

In my case, after I hit D it left the latest saved version intact and deleted the .swp which got created because I exited VIM incorrectly

.MERGE_MSG.swp is open in your git, you just need to delete this .swp file. In my case I used following command and it worked fine.

rm .MERGE_MSG.swp

I've also had this error when trying to pull the changes into a branch which is not created from the upstream branch from which I'm trying to pull.

Eg - This creates a new branch matching night-version of upstream

git checkout upstream/night-version -b testnightversion

This creates a branch testmaster in local which matches the master branch of upstream.

git checkout upstream/master -b testmaster 

Now if I try to pull the changes of night-version into testmaster branch leads to this error.

git pull upstream night-version //while I'm in `master` cloned branch

I managed to solve this by navigating to proper branch and pull the changes.

git checkout testnightversion
git pull upstream night-version // works fine.