text writing: what is the recommended wording for a generic error message?

A good error message should:

  1. Let you know what is the problem.
  2. Make you feel that there is something you can do about it.
  3. Speak like a human, and be a consistent extension of the personality of the rest of the application.

For generic error messages, you can not do much about the first point, but You can do something about the other two..

Do something that allows the user to know the problem. it is not being ignored. Allow them to take some action, such as sending the records or sending a bug report. You can also inform them that automatic measures have already been taken and that your technical staff has been automatically notified that this error occurred and is working on it.

Then, in the way they are told, you must express the message in speak human and keep the consistent tone with the rest of the site (which should be appropriate for your audience). If your site is ludic, use a playful error message. If it is a medical service, make it completely professional.

So the examples are:

Ups! Something went wrong!
Help us improve your experience by sending an error report

or

The application has encountered an unknown error.
It seems that it has not affected your data, but our technical staff has been automatically notified and we will analyze it with the greatest urgency.

or

Damn gerbils have stopped running again! Someone has been sent to hit them with a sharp stick.