.....exited due to signal 4 (SIGILL)

(Mac G4, OS 10.2.6, Project Builder 2.0.1, Interface Builder 2.3)

I am new to AS. I created a new project, a simple app to convert dollar to euro. I created this on the desktop. Everything worked OK. Then I copied the project to another location.
One day, I wanted to do some modifications so I made a duplicate of the project on the desktop. I started the project and clicked build/run. Everything still worked OK. Then I doubleClicked the MainMenu.nib icon to go to the Interface builder. I changed nothing, I only saved by pressing command-S.
Back in the Interface builder I clicked on Build and run.
The app launched, I executed the app, and then it crashed.
I got the following message: “…exited due to signal 4 (SIGILL)”
At this point my entire project was ruined.
DoubleClicking the application caused a crash (Unexpected error…)
I changed nothing, only saved the project in the Interface Builder,

This happens with all my projects so I must have made some error.

Could anyone please tell me what I have done wrong.

John dh