A curious script editor error on saving a stack

[Medard]

As I was testing some scripts on a demo stack, I got a curious error...

It seems that this error lies in the script editor; 
a figure worthing 1000 words, please go and see here:

http://medard.on-rev.com/tempo/erreur_livecode.PNG

I quitted LC a number of times, saved the stack under a new name, with
no luck...

LiveCode 4.5 on Mac OS X 10.6.5