Comment 1 for bug 514198

Each student should be able to create and use a key called "mykey" as long as they're unique users with unique keys on a give machine (or separate machines).

What do you mean by "stopped working"?

Did the user have a running instance that they were able to login with that key, and then later, couldn't log in with the same key to the same running instance?

Or, rather, did they create and use instances with that key, and then later, create instances but not be able to use that key?