Failed to lock refs/heads/master

I am relativly new to git and am facing this problem. The git push command
shows the error below. I will explain to you from the begining what i had
been trying to do . I created a submodule, commited and pushed it. The push
throws the error below.

http://git.661346.n2.nabble.com/file/n7562253/Git_Problem.png 

After that i tried some solutions but none of them worked. I will also
explain breifly what i have been trying

1 : From the bitbucket repo i noticed there are some danggling commits (the
red arrow in picture 2) so i gave the following commands to solve that git
gc and git prune.

2: I also tried commands like git revert HEAD and git push origin HEAD
--force but none seem to worked..

http://git.661346.n2.nabble.com/file/n7562253/Git_Problem_2.png 

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