Cannot be pressed with Mercurial: abort: error: ''

Question

I'm trying to push my changes to the Mercurial Bitbucket.org repository, but when clicked, it unexpectedly breaks with the next empty error

abort: error: '' 

What does it mean? How can I avoid this error?

Note : based on my attempts, push does not always work. Sometimes it ends correctly. But I want to know what this error means. I can not try again and again until the press stops.