When I try to login, it says login failed. I am pretty sure that credentials are correct.
Short answer: This issue has been fixed and a new version should be available soon. You should be able to login again then.
Long answer: Coursera does not provide any public API (yet), so we have to parse data directly from the website. Every time they make a change, it may potentially break the app (like now). I am doing my best to keep up with this, going through the Apple review process every single time.
Good news is, I am cleaning up code to improve this (and I may bring more good stuff soon as well) so stay tuned.