What I know about primitiveChangeClassTo: is that your new class should 
have the same format as the previous one.
Else it is dangerous as mentioned by the comment of the primitive

Stef

> Storing a LargePositiveInteger in GOODS with WriteBarrier works, 
> whereas when I try to step through the appropriate code in 
> WriteBarrier, the primitive fails. Running the following code in a 
> workspace gets the same error. Anyone knows why? Thanks.
>
> ========
> x := 123456789012.
> wb := WriteBarrier new.
> x primitiveChangeClassTo: (wb barrierClassForClass: x class) basicNew
> ========
>
> -- 
> Regards
> HweeBoon
> MotionObj
>