GitHub App & Heroku — fatal: Reference has invalid format: 'refs/remotes/heroku/master'

I am using the Git app and every time I open a certain repo I get this error:

Any help would be great. Thanks.

Solution

You're certainly using Dropbox to sync your project among multiple computers. While performing the sync, the tool detected a conflict between two files and created a backup with the suffix (COMPUTER_NAME's conflicted copy DATE).

Unfortunately, the conflicted file is a reference, and according to Git naming convention, the name of a reference cannot contain spaces. See git check-ref-format man page for more information about rules describing how references should be named.

As references are only text files containing pointers to a commit Sha or another reference, fixing this is not a complex issue.

In order to resolve this, the following steps should be followed:

Within your project directory, open both the .git/refs/remotes/heroku/master and the .git/refs/remotes/heroku/master (Richard Burton's conflicted copy 2012-11-24) files in a text editor and decide which content is the most up to date (ie. which is the real tip of the remote master branch on Heroku).
Copy the correct SHA and paste it in the file named .git/refs/remotes/heroku/master
Drop the .git/refs/remotes/heroku/master (Richard Burton's conflicted copy 2012-11-24) file.

Note: you may have other files in conflict. In order to be thorough, launch a recursive search in your project for files which name contains conflicted copy

Note 2: git ls-remote --heads heroku may be handy in this situation as it will request the remote repository about its known branchs.