Using VS 2015.
The full error is:
"Cannot pull because there are uncommitted changes. Commit or undo your
changes before pulling again. See the Output window for details."
So annoying. This happens a lot when trying to pull.
Install Git Bash.
In Windows Explorer, navigate to the directory where your project is and right click.
$ git status
On branch somebranch
Check you are on the right branch. You will get messages about the difference with master.
$ git pull
Back to VS. Now you get a message about files being updated outside of VS.
Just "Reload all".