Well, illegal opcode means that it is not a legal opcode :smileyhappy:.
Eventually (if debugging in RAM) the code got changed (corrupted), or more probably (especially when debugging in flash) the core jumped to non code (constants, data, variables, non memory areas...). There are many reasons how this could happen (stack too small, array overflow, uninitialized variables,... so its a bit hard to guess remotely why the core ends up there.
I guess the illegal breakpoint message means pretty much the same thing, that the code is executing non code.
What is at those addresses (check the map file).
Also make sure the initial loading/flashing did succeed properly.
