It's not working.
You've probably heard this a few times from users. Very rarely will a user send you a message regarding an issue that tells you what they are truly experiencing with an application, dataset, and so on. Keep in mind that they aren't as intimately familiar with all the aspects and functionalities of your system; they might only use one tool in one application, so when that one facet isn't working right for them, they see it as broken, and that's fine. Part of your job is to calmly and politely walk through their workflow with them and find out exactly what they were doing when things didn't go as they expected. Sometimes, this can be done over email; sometimes, it might be best to do it over a phone call; and, sometimes you might need to look over their shoulder to watch them reproduce the issue. However you do it, you need to translate it's not working into some actionable information that you can then use to start working on the issue. Some things to...