I describe the situation:
I removed a teacher(T1) from the "Teachers" dialog box, and then I tried to rename another teacher(T2) by the same symbol of the teacher removed(T1).
At that time and when I click the Ok button. FET does not respond. It crash.
This bug reproduces with all versions of fet, unfortunately
I attach below a screen shot of the bug.
Hmmm.... I can't reproduce. I will check the source. Maybe you can sent me your file, so i can hopefully reproduce it.
If the teachers have attached not available constraints. I will release right away (in hopefully 1 hour).
I released the three versions (official, Algeria, and Morocco), hopefully bug fixed. Thank you for the report!