TCM is not a perfect program and it is under continuous development. So it can happen that the internal graph, a shape view or a table in the editor becomes inconsistent . Therefore, assertions are built-in in the code. They are used for internal consistency checking or for checking if a command can be executed safely. They prevent harm as much as possible. When these assertions fail, warning messages are added to the message log dialog and the message log dialog is displayed. The messages contain amongst others the source code file and line number where the assertion was checked and failed. This does not say much to an ordinary user, but they can be very helpful for us to fix bugs. So when you send a bug report to us, you should include these assertion failed messages. Furthermore, as the diagram file is in ASCII, you can also include a faulty document as plain text in your e-mail.