I am fairly new to git yet currently using it to manage our code in a team environment. I had some rebasing issues and I fixed them using
git ch
I had this problem and none of above advises helped me. I was able to fetch everything correctly. But push always failed. It was a local repository located on windows directory with several clients working with it through VMWare shared folder driver. It appeared that one of the systems locked Git repository for writing. After stopping relevant VMWare system, which caused the lock everything repaired immediately. It was almost impossible to figure out, which system causes the error, so I had to stop them one by one until succeeded.