While trying to clone an already existing repository from gitlab into my local drive. I used the format
$ git clone https://github.com/libgit2/libgit2 mylibgit
I had similar problem. Just corrected(removed git@ and port number) URL in .git/config file and it worked.
[remote "origin"] url = https://git@gitlab.com:xxxxx/yyyyyy/
To
[remote "origin"] url = https://gitlab.com/yyyyyy/